In preparation for the forthcoming spec changes for #6977.
While at it, modernize existing File example that dates
back all the way to commit 18c5b488a3.
Change-Id: Id10e4df0513e3de15bd58867222923eefa9473ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/187978
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
The spec was not very precise as to what happens with respect to sharing
if a sliced operand is (a pointer to) an array. Added a small clarification
and a supporting example.
Fixes#31689.
Change-Id: Ic49351bec2033abd3f5428154ec3e9a7c2c9eaa5
Reviewed-on: https://go-review.googlesource.com/c/go/+/177139
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Add a small paragraph and example pointing out
the difference for the case where T is a slice
or map. This is a common error for Go novices.
Fixes#29425.
Change-Id: Icdb59f25361e9f6a09b190fbfcc9ae0c7d90077b
Reviewed-on: https://go-review.googlesource.com/c/go/+/176338
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
The very first paragraph on "Package initialization" stated that
"variables are initialized in declaration order, but after any
variables they might depend on". This phrasing was easily
misread as "declaration order is the first sorting criteria"
and then contradicted what the subsequent paragraphs spelled
out in precise detail.
Instead, variable initialization proceeds by repeatedly determining
a set of ready to initialize variables, and then selecting from that
set the variable declared earliest. That is, declaration order is the
second sorting criteria.
Also, for the purpose of variable initialization, declarations
introducing blank (_) variables are considered like any other
variables (their initialization expressions may have side-effects
and affect initialization order), even though blank identifiers
are not "declared".
This CL adds clarifying language regarding these two issues
and the supporting example.
Both gccgo and go/types implement this behavior. cmd/compile
has a long-standing issue (#22326).
The spec also did not state in which order multiple variables
initialized by a single (multi-value) initialization expression are
handled. This CL adds a clarifying paragraph: If any such variable
is initialized, all that declaration's variables are initialized at
the same time.
This behavior matches user expectation: We are not expecting to
observe partially initialized sets of variables in declarations
such as "var a, b, c = f()".
It also matches existing cmd/compile and go/types (but not gccgo)
behavior.
Finally, cmd/compile, gccgo, and go/types produce different
initialization orders in (esoteric) cases where hidden (not
detected with existing rules) dependencies exist. Added a
sentence and example clarifying how much leeway compilers have
in those situations. The goal is to preserve the ability to
use static initialization while at the same time maintain
the relative initialization order of variables with detected
dependencies.
Fixes #31292.
Updates #22326.
Change-Id: I0a369abff8cfce27afc975998db875f5c580caa2
Reviewed-on: https://go-review.googlesource.com/c/go/+/175980
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This CL documents the new binary and octal integer literals,
hexadecimal floats, generalized imaginary literals and digit
separators for all number literals in the spec.
Added empty lines between abutting paragraphs in some places
(a more thorough cleanup can be done in a separate CL).
A minor detail: A single 0 was considered an octal zero per the
syntax (decimal integer literals always started with a non-zero
digit). The new octal literal syntax allows 0o and 0O prefixes
and when keeping the respective octal_lit syntax symmetric with
all the others (binary_lit, hex_lit), a single 0 is not automatically
part of it anymore. Rather than complicating the new octal_lit syntax
to include 0 as before, it is simpler (and more natural) to accept
a single 0 as part of a decimal_lit. This is purely a notational
change.
R=Go1.13
Updates #12711.
Updates #19308.
Updates #28493.
Updates #29008.
Change-Id: Ib9fdc6e781f6031cceeed37aaed9d05c7141adec
Reviewed-on: https://go-review.googlesource.com/c/go/+/161098
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This text changed in CL 139099 to add "explicit" in front of "conversion".
But now "explicit conversion or assignment" reads like it might mean
"explicit [conversion or assignment]" when what is meant is
"[explicit conversion] or assignment". To make clear that explicit does
not apply to assignment, use "assignment or explicit conversion".
Change-Id: I8ff7a5b3ecd9f562793502fa6808242f22264f28
Reviewed-on: https://go-review.googlesource.com/c/149340
Reviewed-by: Robert Griesemer <gri@golang.org>
Adjusted spec to explicitly define the string length as the
number of bytes of the string; the prose now matches the prose
for arrays. Made analogous change for slices.
Fixes#28736.
Change-Id: I47cab321c87de0a4c482f5466b819b2cc8993fd1
Reviewed-on: https://go-review.googlesource.com/c/149077
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
The spec currently provides a syntactic rule for receiver base types,
and a strict reading of those rules prohibits the use of type aliases
referring to pointer types as receiver types.
This strict interpretation breaks an assumed rule for aliases, which
is that a type literal can always be replaced by an alias denoting
that literal.
Furthermore, cmd/compile always accepted this new formulation of the
receiver type rules and so this change will simply validate what has
been implemented all along.
Fixes#27995.
Change-Id: I032289c926a4f070d6f7795431d86635fe64d907
Reviewed-on: https://go-review.googlesource.com/c/142757
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
The spec used the term "conversion" somewhat indiscriminately for
explicit conversions that appear literally in the source, and implicit
conversions that are implied by the context of an expression.
Be clearer about it by defining the terms.
Also, state that integer to string conversions of the form string(x)
are never implicit. This clarifies situations where implicit conversions
might require an integer to change to a string (but don't and never have
done so). See line 3948.
Fixes#26313.
Change-Id: I8939466df6b5950933ae7c987662ef9f88827fda
Reviewed-on: https://go-review.googlesource.com/c/139099
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Fixes#27802.
Change-Id: I7ea9f7279300a55b0cb851893edc591a6f84e324
Reviewed-on: https://go-review.googlesource.com/136758
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This reverts commit 4b06d9d727.
Reason for revert: It's a reference to a legendary article
from the Journal of Irreproducible Results.
Updates golang/go#24451
Change-Id: I0288177f4e286bd6ace5774f2e5e0acb02370305
Reviewed-on: https://go-review.googlesource.com/101495
Reviewed-by: Andrew Bonventre <andybons@golang.org>
The fourth example for map indexing states you have a map of type [K]V
and attempts to read in a variable of type T. Further, the example
is meant to showcase the boolean return variable saying whether the
map contained a key, but overrides to type T. This will not compile.
Changed last updated date to February 18
Fixes: #23895
Change-Id: I63c52adbcd989afd4855e329e6c727f4c01f7881
Reviewed-on: https://go-review.googlesource.com/94906
Reviewed-by: Robert Griesemer <gri@golang.org>
The EBNF production
Function = Signature FunctionBody .
was used in FunctionDecl, MethodDecl, and FunctionLit, but only
for the latter it shortened the syntax slightly.
This change "inlines" Function which simplifies FunctionDecl and
MethodDecl and gets rid of the Function production.
This has no impact on the specified language. Also, the Function
production is never referred to by the prose, so it's safe to
remove it from the spec.
Finally, neither go/ast nor go/parser have a representation of
this production via a corresponding node or parse function, so
no possibly valuable documentation is lost, either.
Change-Id: Ia2875d31c6ec2d2079081ef481e50bad4f43c694
Reviewed-on: https://go-review.googlesource.com/91515
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
When we introduced the notion of alias type declarations, we renamed
"named type" to "defined type" to avoid confusion with types denoted
by aliases and thus are also types with names, or "named types".
Some of the old uses of "named types" remained; this change removes
them.
Now the spec consistently uses the terms:
- "defined type" for a type declared via a type definition
- "type name" for any name denoting an (alias or defined) type
- "alias" for a type name declared in an alias declaration
New prose is encouraged to avoid the term "named type" to counter-
act further confusion.
Fixes#23474.
Change-Id: I5fb59f1208baf958da79cf51ed3eb1411cd18e03
Reviewed-on: https://go-review.googlesource.com/89115
Reviewed-by: Rob Pike <r@golang.org>
Fixes#23443.
Change-Id: If60c39b582ee5308e9fa902f93c1b6ae7890346c
Reviewed-on: https://go-review.googlesource.com/87975
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Every few months we get a new error report claiming that there
is a typo in the spec related to this specific example. Clearly,
the fact that two types with the same identifier are identical
seems exceedingly obvious to readers; thus the example seems not
worth the trouble. Removing it.
For #9226.
For #22202.
For #22495.
For #23096.
For #23409.
There may be more.
Change-Id: I003ba79dc460ffb028a4ecb5f29efd60f2551912
Reviewed-on: https://go-review.googlesource.com/87417
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
The spec refers to a map's key and element types; thus the respective
values are "keys" and "elements". Also, a map value is the value of
the entire map.
Similar fix for channels, where appropriate.
Fixes#23254.
Change-Id: I6f03ea6d86586c7b0b3e84f0c2e9446b8109fa53
Reviewed-on: https://go-review.googlesource.com/85999
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
A method expression is of the form T.m where T is a type and m
is a method of that type. The spec restricted T essentially to
a type name. Both cmd/compile and go/types accepted any type
syntactically, and a method expression was really just a form
of a selector expression x.f where x denotes a type.
This CL removes the spec syntax restriction from MethodExpr
to match the actual implementation. It also moves MethodExpr
from Operand to PrimaryExpr, because that's what it is.
It still keeps the separate notion of MethodExpr even though
it looks just like a selector expresion, since a MethodExpr
must start with a type rather than a value, and the spec's
syntax expresses this bit of semantics via distinct productions
(e.g., conversions look like calls but also must start with
a type).
Fixes#9060.
Change-Id: Idd84655b5b4f85d7ee53ebf749f73f0414a05f4a
Reviewed-on: https://go-review.googlesource.com/73233
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
https://golang.org/cl/71750 specifies iota values as indices,
thus making them independent from nested constant declarations.
This CL removes some of the comments in the examples that were
still referring to the old notion of iotas being incremented
and reset.
As an aside, please note that the spec still permits the use
of iota in a nested function (like before). Specifically, the
following cases are permitted by the spec (as before):
1) const _ = len([iota]int{})
2) const _ = unsafe.Sizeof(func(){ _ = iota })
For #15550.
Change-Id: I9e5fec75daf7b628b1e08d970512397e9c348923
Reviewed-on: https://go-review.googlesource.com/71912
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Issue #15550 is clearly an esoteric case but the spec was silent
about it and we had diverging implementations. By making `iota`
and index that is relative to the respective constant declaration,
nested const declarations won't affect outer values of `iota`.
cmd/compile and go/types already follow this semantics.
Fixes#15550.
Change-Id: If138189e3ea4373f8ba50ac6fb1d219b481f8698
Reviewed-on: https://go-review.googlesource.com/71750
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Fixes#22258.
Change-Id: I43e68f1cf3163e1a041ebff2734ff2cb7943f695
Reviewed-on: https://go-review.googlesource.com/71431
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Nowhere in the spec did we mention the import path for package
unsafe. Now we do.
Fixes#22308.
Change-Id: Ifd42c873188e898c597cdee4284e7a9d234a9282
Reviewed-on: https://go-review.googlesource.com/71373
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
When we introduced the distinction between "defined" and "alias" types
we retained the notion of a "named" type (any type with a name). The
predeclared types (which all have names) simply remained named types.
This CL clarifies the spec by stating excplicitly which predeclared
types are defined types (or at least "act" like defined types), and
which ones are alias types.
Fixes#21785.
Change-Id: Ia8ae133509eb5d738e6757b3442c9992355e3535
Reviewed-on: https://go-review.googlesource.com/64591
Reviewed-by: Russ Cox <rsc@golang.org>
The spec is not conclusive about whether a non-constant shift of
certain untyped constant left operands is valid when the shift
expression appears as an index in an index or slice expression,
or as a size in a `make` function call.
Despite identical spec rules in all these cases, cmd/compile accepts
make([]byte, 1.0 << s)
but pronounces an error for
a[1.0 << s]
(go/types accepts both).
This change clarifies the spec by explicitly stating that an
untyped constant left operand in a non-constant shift (1.0 in
the above examples) will be given type `int` in these contexts.
A separate issue #21693 addresses the cmd/compile bug.
Fixes#14844.
Change-Id: I4b52125e487a607fae377fcbed55463cdce9836c
Reviewed-on: https://go-review.googlesource.com/60230
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
The last sentence in the section on slice expressions could be read
as if it might apply to strings. Changed the sentence a bit to
emphasize its applicability to slices only. See also the issue for
more background.
Fixes#19220.
Change-Id: I8551f34230e4ed93f951e7b871cc81f54a5874a9
Reviewed-on: https://go-review.googlesource.com/59890
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Throughout the spec we use the notion of a constant x being
representable by a value of type T. While intuitively clear,
at least for floating-point and complex constants types, the
concept was not well-defined. In the section on Conversions
there was an extra rule for floating-point types only and it
missed the case of floating-point values overflowing to an
infinity after rounding.
Since the concept is important to Go, and a compiler most
certainly will have a function to test "representability",
it seems warranted to define the term explicitly in the spec.
This change introduces a new entry "Representability" under
the section on "Properties of types and values", and defines
the term explicitly, together with examples.
The phrase used is "representable by" rather than "representable as"
because the former use is prevalent in the spec.
Additionally, it clarifies that a floating-point constant
that overflows to an infinity after rounding is never
representable by a value of a floating-point type, even though
infinities are valid values of IEEE floating point types.
This is required because there are not infinite value constants
in the language (like there is also no -0.0) and representability
also matters for constant conversions. This is not a language
change, and type-checkers have been following this rule before.
The change also introduces links throughout the spec to the new
section as appropriate and removes duplicate text and examples
elsewhere (Constants and Conversions sections), leading to
simplifications in the relevant paragraphs.
Fixes#15389.
Change-Id: I8be0e071552df0f18998ef4c5ef521f64ffe8c44
Reviewed-on: https://go-review.googlesource.com/57530
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
The enumeration of numeric types missed the complex types.
Clarify by removing the explicit enumeration and referring
to numeric types instead.
Fixes#21579.
Change-Id: If36c2421f8501eeec82a07f442ac2e16a35927ba
Reviewed-on: https://go-review.googlesource.com/58491
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
The old wording seemed to imply that nil is a kind of type.
Slightly reworded for clarity.
Fixes#21580.
Change-Id: I29898bf0125a10cb8dbb5c7e63ec5399ebc590ca
Reviewed-on: https://go-review.googlesource.com/58490
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Rob Pike <r@golang.org>
The old comment for the example
type PtrMutex *Mutex
talked about the method set of the base type of PtrMutex.
It's more direct and clearer to talk about the underlying
type of PtrMutex for this specific example.
Also removed link inside pre-formatted region of text.
Fixes#20900.
Change-Id: Ie37340e53670e34ebe13e780ba8ccb1bba67795c
Reviewed-on: https://go-review.googlesource.com/55070
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
For non-constant shifts with an untyped constant shift count, the
spec only said that it must "be converted to unsigned integer type".
go/types accepts any (arbitrarily large) integer value. Both cmd/compile
and gccgo require that the shift count be representable as a uint value
in that case (if the shift count is typed, it may be any unsigned integer
type).
This change adjusts the spec to state what the compilers have been doing
all along. The new wording matches similar rules elsewhere (e.g., for
untyped array and slice indices). Also, while technically this is a
restriction (we could permit arbitrarily large shift counts), in practice
this is irrelevant.
Fixes#14822.
Change-Id: Ia75834c67483cf761c10025c8df758f225ef67c2
Reviewed-on: https://go-review.googlesource.com/45072
Reviewed-by: Ian Lance Taylor <iant@golang.org>
A pointer type of underlying type unsafe.Pointer can be used in
unsafe conversions. Document unfortunate status quo.
Fixes#19306.
Change-Id: I28172508a200561f8df366bbf2c2807ef3b48c97
Reviewed-on: https://go-review.googlesource.com/42132
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Added a paragraph and examples explaining when an implementation
may use fused floating-point operations (such as FMA) and how to
prevent operation fusion.
For #17895.
Change-Id: I64c9559fc1097e597525caca420cfa7032d67014
Reviewed-on: https://go-review.googlesource.com/40391
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
The section on map literals mentions constant map keys but doesn't say
what happens for equal non-constant map keys - that is covered in the
section on evaluation order. Added respective link for clarity.
Fixes#19689.
Change-Id: If9a5368ba02e8250d4bb0a1d60d0de26a1f37bbb
Reviewed-on: https://go-review.googlesource.com/38598
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
The (original) section on "Operators and Delimiters" introduced
superfluous terminology ("delimiter", "special token") which
didn't matter and was used inconsistently.
Removed any mention of "delimiter" or "special token" and now
simply group the special character tokens into "operators"
(clearly defined via links), and "punctuation" (everything else).
Fixes#19450.
Change-Id: Ife31b24b95167ace096f93ed180b7eae41c66808
Reviewed-on: https://go-review.googlesource.com/38073
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Rob Pike <r@golang.org>
To avoid confusion caused by the term "named type" (which now just
means a type with a name, but formerly meant a type declared with
a non-alias type declaration), a type declaration now comes in two
forms: alias declarations and type definitions. Both declare a type
name, but type definitions also define new types.
Replace the use of "named type" with "defined type" elsewhere in
the spec.
For #18130.
Change-Id: I49f5ddacefce90354eb65ee5fbf10ba737221995
Reviewed-on: https://go-review.googlesource.com/36213
Reviewed-by: Rob Pike <r@golang.org>
First steps towards defining type aliases in the spec.
This is a nomenclature clarification, not a language change.
The spec used all three terms 'embedded type', 'anonymous field',
and 'embedded field'. Users where using the terms inconsistently.
The notion of an 'anonymous' field was always misleading since they
always had a de-facto name. With type aliases that name becomes even
more important because we may have different names for the same type.
Use the term 'embedded field' consistently and remove competing
terminology.
For #18130.
Change-Id: I2083bbc85788cab0b2e2cb1ff58b2f979491f001
Reviewed-on: https://go-review.googlesource.com/35108
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
This matches what we already do for switch statements and makes
this large section more visibly organized. No other changes besides
introducing the titles.
Fixes#4486.
Change-Id: I73f274e4fdd27c6cfeaed79090b4553e57a9c479
Reviewed-on: https://go-review.googlesource.com/33410
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
- organize examples better
- add an example illustrating behavior if element type is a named pointer type
- both compilers and go/types (per https://go-review.googlesource.com/33358)
follow this now
See the issue for detailed discussion.
Fixes#17954.
Change-Id: I8d90507ff2347d9493813f75b73233819880d2b4
Reviewed-on: https://go-review.googlesource.com/33361
Reviewed-by: Rob Pike <r@golang.org>
A 16bit binary exponent permits a constant range covering roughly the range
from 7e-9865 to 7e9863 which is more than enough for any practical and
hypothetical constant arithmetic.
Furthermore, until recently cmd/compile could not handle very large exponents
correctly anyway; i.e., the chance that any real programs (but for tests that
explore corner cases) are affected are close to zero.
Finally, restricting the minimum supported range significantly reduces the
implementation complexity in an area that hardly matters in reality for new
or alternative spec-compliant implementations that don't or cannot rely on
pre-existing arbitratry precision arithmetic packages that support a 32bit
exponent range.
This is technically a language change but for the reasons mentioned above
this is unlikely to affect any real programs, and certainly not programs
compiled with the gc or gccgo compilers as they currently support up to
32bit exponents.
Fixes#13572.
Change-Id: I970f919c57fc82c0175844364cf48ea335f17d39
Reviewed-on: https://go-review.googlesource.com/17711
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
This simply documents the status quo accepted by cmd/compile, gccgo,
and go/types. The new language matches the language used for indices
of index expressions for arrays and slices.
Fixes#16679.
Change-Id: I65447889fbda9d222f2a9e6c10334d1b38c555f0
Reviewed-on: https://go-review.googlesource.com/30474
Reviewed-by: Rob Pike <r@golang.org>
This is a backwards-compatible language change.
Per the proposal (#16085), the rules for conversions are relaxed
such that struct tags in any of the structs involved in the conversion
are ignored (recursively).
Because this is loosening the existing rules, code that compiled so
far will continue to compile.
For #16085.
Fixes#6858.
Change-Id: I0feef651582db5f23046a2331fc3f179ae577c45
Reviewed-on: https://go-review.googlesource.com/24190
Reviewed-by: Russ Cox <rsc@golang.org>
See the issue below for details.
Fixes#16794.
Change-Id: I7e338089fd80ddcb634fa80bfc658dee2772361c
Reviewed-on: https://go-review.googlesource.com/27356
Reviewed-by: Ian Lance Taylor <iant@golang.org>
The enumerations didn't include the syntactic form where the lhs is
full variable declaration with type specification, as in:
var x, ok T = ...
Fixes#15782.
Change-Id: I0f7bafc37dc9dcf62cdb0894a0d157074ccd4b3e
Reviewed-on: https://go-review.googlesource.com/27670
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
The changes match the existing compilers, and assume an adjusted
spec (per issue #16794).
Fixes#15686.
Change-Id: I72677ce75888c41a8f3c2963117a2f2d5501c42b
Reviewed-on: https://go-review.googlesource.com/27290
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Both compilers and also go/types don't permit duplicate types in
type switches; i.e., this spec change is documenting a status quo
that has existed for some time.
Furthermore, duplicate nils are not accepted by gccgo or go/types;
and more recently started causing a compiler error in gc. Permitting
them is inconsistent with the existing status quo.
Rather than making it an implementation restriction (as we have for
expression switches), this is a hard requirement since it was enforced
from the beginning (except for duplicate nils); it is also a well
specified requirement that does not pose a significant burden for
an implementation.
Fixes#15896.
Change-Id: If12db5bafa87598b323ea84418cb05421e657dd8
Reviewed-on: https://go-review.googlesource.com/23584
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Note that the spec already makes that point with a comment in the very first
example for struct field tags. This change is simply stating this explicitly
in the actual spec prose.
- gccgo and go/types already follow this rule
- the current reflect package API doesn't distinguish between absent tags
and empty tags (i.e., there is no discoverable difference)
Fixes#15412.
Change-Id: I92f9c283064137b4c8651630cee0343720717a02
Reviewed-on: https://go-review.googlesource.com/22391
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Per a suggestion from mdempsky.
Both gc and gccgo consider a statement list as terminating if the
last _non_empty_ statement is terminating; i.e., trailing semis are
ok. Only gotype followed the current stricter rule in the spec.
This change adjusts the spec to match gc and gccgo behavior. In
support of this change, the spec has a matching rule for fallthrough,
which in valid positions may be followed by trailing semis as well.
For details and examples, see the issue below.
Fixes#14422.
Change-Id: Ie17c282e216fc40ecb54623445c17be111e17ade
Reviewed-on: https://go-review.googlesource.com/19981
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
The () parentheses grouped wrongly. Removed them completely in
favor of separate 2- and 3-index slice alternatives which is
clearer.
Fixes#14477.
Change-Id: I0b7521ac912130d9ea8740b8793b3b88e2609418
Reviewed-on: https://go-review.googlesource.com/19853
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Slightly rephrased sentence to emphasize the contents of the
Unicode categories w/o repeating the full category name each
time.
Fixes#13414.
Change-Id: Icd32ff1547fa81e866c5937a631c3344bb6087c6
Reviewed-on: https://go-review.googlesource.com/18265
Reviewed-by: Rob Pike <r@golang.org>
The proper term is "untyped boolean".
Change-Id: Id871164190a03c64a8a8987b1ad5d8653a21d96e
Reviewed-on: https://go-review.googlesource.com/16135
Reviewed-by: Robert Griesemer <gri@golang.org>
The spec defines precise numeric constants which do not overflow.
Consequently, +/-Inf and NaN values were excluded. The case was not
clear for -0.0 but they are mostly of interest to determine the sign
of infinities which don't exist.
That said, the conversion rules explicitly say that T(x) (for a numeric
x and floating-point type T) is the value after rounding per IEEE-754.
The result is constant if x is constant. Rounding per IEEE-754 can
produce a -0.0 which we cannot represent as a constant.
Thus, the spec is inconsistent. Attempt to fix the inconsistency by
adjusting the rounding rule rather than letting -0.0 into the language.
For more details, see the issue below.
Open to discussion.
Fixes#12576.
Change-Id: Ibe3c676372ab16d9229f1f9daaf316f761e074ee
Reviewed-on: https://go-review.googlesource.com/14727
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
The prose discussing composite literals referred to the composite
literal type with 'LiteralType', denoting the literal type's EBNF
production explicitly. Changed 'LiteralType' to 'literal type' to
remove the literal (no pun intended) connection and instead mean
the underlying type. Seems a simpler and more readable change
than referring to the underlying type everywhere explicitly.
Fixes#12717.
Change-Id: I225df95f9ece2664b19068525ea8bda5ca05a44a
Reviewed-on: https://go-review.googlesource.com/14851
Reviewed-by: Rob Pike <r@golang.org>
First step towards cleaning up the operator section - no language
changes. Specifically:
- Grouped arithmetic operations by types (integer, floating-point,
string), with corresponding h4 headings.
- Changed Operator precedence title from h3 to h4.
- Moved Integer Overflow section after integer operations and changed
its title from h3 to h4.
This puts things that belong together closer. No heading id's were
lost (in case of references from outside the spec).
Change-Id: I6b349ba8d86a6ae29b596beb297cc45c81e69399
Reviewed-on: https://go-review.googlesource.com/13143
Reviewed-by: Rob Pike <r@golang.org>
The spec didn't specify several aspects of expression switches:
- The switch expression is evaluated exactly once.
- Switch expressions evaluating to an untyped value are converted
to the respective default type before use.
- An (untyped) nil value is not permitted as expression switch
value. (We could permit it relatively easily, but gc doesn't,
and disallowing it is in symmetry with the rules for var decls
without explicit type and untyped initializer expressions.)
- The comparison x == t between each case expression x and
switch expression value t must be valid.
- (Some) duplicate constant case expressions are not permitted.
This change also clarifies the following issues:
4524: mult. equal int const switch case values should be illegal
-> spec issue fixed
6398: switch w/ no value uses bool rather than untyped bool
-> spec issue fixed
11578: allows duplicate switch cases -> go/types bug
11667: int overflow in switch expression -> go/types bug
11668: use of untyped nil in switch -> not a gc bug
Fixes#4524.
Fixes#6398.
Fixes#11668.
Change-Id: Iae4ab3e714575a5d11c92c9b8fbf027aa706b370
Reviewed-on: https://go-review.googlesource.com/12711
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
The document `doc/go_spec.html` uses "preceeding" instead of the word
"preceding" in one place.
Fixed another occurrence in `src/go/types/typexpr.go`.
Change-Id: Ic67f62026b5c9d002c5c5632299f14ecac8b02ae
Reviewed-on: https://go-review.googlesource.com/12354
Reviewed-by: Ian Lance Taylor <iant@golang.org>
No need to update the date; this is not a spec change.
Change-Id: I10a31234ed985c59e5d9b5328664a36661cef31e
Reviewed-on: https://go-review.googlesource.com/11531
Reviewed-by: Andrew Gerrand <adg@golang.org>
Suggested by mdempsky (see also issue #11161).
Change-Id: I1ab28febe19b7a092029499015073ce8749b4d99
Reviewed-on: https://go-review.googlesource.com/10960
Reviewed-by: Ian Lance Taylor <iant@golang.org>
- no "visible" change to spec but for updated date
- retired several outdated TODO items
- filed non-urgent issues 10953, 10954, 10955 for current TODOs
Change-Id: If87ad0fb546c6955a6d4b5801e06e5c7d5695ea2
Reviewed-on: https://go-review.googlesource.com/10382
Reviewed-by: Ian Lance Taylor <iant@golang.org>
The spec explains later in the "Operator precedence" section that *
has a higher precedence than +, but the current production rule
requires that "1 + 2 * 3" be parsed as "(1 + 2) * 3", instead of the
intended "1 + (2 * 3)".
The new production rule better matches cmd/internal/gc/go.y's grammar:
expr:
uexpr
| expr LOROR expr
| expr LANDAND expr
| ...
Fixes#10151.
Change-Id: I13c9635d6ddf1263cafe7cc63e68f3e5779e24ba
Reviewed-on: https://go-review.googlesource.com/9163
Reviewed-by: Robert Griesemer <gri@golang.org>
to map element keys
Composite literals containing element values that are themselves composite
literals may leave away the element's literal types if they are identical
to the enclosing composite literal's element type.
(http://golang.org/ref/spec#Composite_literals)
When we made this change, we forgot to apply the analogous rule to map
literal keys. This change generalizes that rule. Added more examples,
including one showing the recursive application of the elision rules.
This is a fully backward-compatible language change. It was discussed
some time back.
Fixes#8589.
To be submitted once all compilers accept the extension.
Change-Id: I4d45b64b5970f0d5501572945d5a097e64a9458b
Reviewed-on: https://go-review.googlesource.com/2591
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Language clarification.
The existing rules for selector expressions imply
automatic dereferencing of pointers to struct fields.
They also implied automatic dereferencing of selectors
denoting methods. In almost all cases, such automatic
dereferencing does indeed take place for methods but the
reason is not the selector rules but the fact that method
sets include both methods with T and *T receivers; so for
a *T actual receiver, a method expecting a formal T
receiver, also accepts a *T (and the invocation or method
value expression is the reason for the auto-derefering).
However, the rules as stated so far implied that even in
case of a variable p of named pointer type P, a selector
expression p.f would always be shorthand for (*p).f. This
is true for field selectors f, but cannot be true for
method selectors since a named pointer type always has an
empty method set.
Named pointer types may never appear as anonymous field
types (and method receivers, for that matter), so this
only applies to variables declared of a named pointer
type. This is exceedingly rare and perhaps shouldn't be
permitted in the first place (but we cannot change that).
Amended the selector rules to make auto-deref of values
of named pointer types an exception to the general rules
and added corresponding examples with explanations.
Both gc and gccgo have a bug where they do auto-deref
pointers of named types in method selectors where they
should not:
See http://play.golang.org/p/c6VhjcIVdM , line 45.
Fixes#5769.
Fixes#8989.
LGTM=r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/168790043
Not a language change.
This is simply documenting the status quo which permits
builtin function names to be parenthesized in calls; e.g.,
both
len(s)
and
(((len)))(s)
are accepted by all compilers and go/types.
Changed the grammar by merging the details of BuiltinCall
with ordinary Calls. Also renamed the Call production to
Arguments which more clearly identifies that part of the
grammar and also matches better with its counterpart on
the declaration side (Parameters).
The fact that the first argument can be a type (for builtins)
or cannot be a type (for regular function calls) is expressed
in the prose, no need to make the grammar more complicated.
Fixes#9001.
LGTM=iant, r, rsc
R=r, rsc, iant, ken, dave
CC=golang-codereviews
https://golang.org/cl/160570043
Per suggestion from rsc as a result of the dicussion of
(abandoned) CL 153110044.
Fixes#7192.
LGTM=r, rsc, iant
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/163050043
Not a language change.
Several inaccuracies were fixed:
1) A variable declaration may declare more than just one
variable.
2) Variable initialization follows the rules of assignments,
including n:1 assignments. The existing wording implied a 1:1
or n:n rule and generally was somewhat unspecific.
3) The rules for variable declarations with no types and
untyped initialization expressions had minor holes (issue 8088).
4) Clarified the special cases of assignments of untyped values
(we don't just have untyped constants, but also untyped bools,
e.g. from comparisons). The new wording is more direct.
To that end, introduced the notion of an untyped constant's
"default type" so that the same concept doesn't have to be
repeatedly introduced.
Fixes#8088.
LGTM=iant, r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/142320043
The existing spec rules on package initialization were
contradictory: They specified that 1) dependent variables
are initialized in dependency order, and 2) independent
variables are initialized in declaration order. This 2nd
rule cannot be satisfied in general. For instance, for
var (
c = b + 2
a = 0
b = 1
)
because of its dependency on b, c must be initialized after b,
leading to the partial order b, c. Because a is independent of
b but is declared before b, we end up with the order: a, b, c.
But a is also independent of c and is declared after c, so the
order b, c, a should also be valid in contradiction to a, b, c.
The new rules are given in form of an algorithm which outlines
initialization order explicitly.
gccgo and go/types already follow these rules.
Fixes#8485.
LGTM=iant, r, rsc
R=r, rsc, iant, ken, gordon.klaus, adonovan
CC=golang-codereviews
https://golang.org/cl/142880043
The proposed text in the last CL had a comma that was missing from the submitted spec.
LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/150720043
Preparation for fixing issue 5769 (method selectors
do not auto-dereference): The actual fix may require
some cleanups in all these sections, and syntactically,
method expressions and method values are selector
expressions. Moving them next to each other so that
it's easy to see the actual changes (next CL).
No content changes besides the section moves.
LGTM=iant, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/132300043
Technically a language change, this cleanup is a completely
backward compatible change that brings the boolean results
of comma-ok expressions in line with the boolean results of
comparisons: they are now all untyped booleans.
The implementation effort should be minimal (less than a
handfull lines of code, depending how well factored the
implementation of comma-ok expressions is).
Fixes#8189.
LGTM=iant, r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/112320045
golang.org now serves HTTPS with a valid cert, so it's reasonable
that users should click through to the HTTPS versions of *.golang.org
and other known sites.
LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/112650043
This is a fully backward-compatible language change.
There are not a lot of cases in the std library, but
there are some. Arguably this makes the syntax a bit
more regular - any trailing index variable that is _
can be left away, and there's some analogy to type
switches where the temporary can be left away.
Implementation-wise the change should be trivial as
it can be done completely syntactically. For instance,
the respective change in go/parser is a dozen lines
(see https://golang.org/cl/112970044 ).
Fixes#6102.
LGTM=iant, r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/104680043
This CL removes the special syntax for method receivers and
makes it just like other parameters. Instead, the crucial
receiver-specific rules (exactly one receiver, receiver type
must be of the form T or *T) are specified verbally instead
of syntactically.
This is a fully backward-compatible (and minor) syntax
relaxation. As a result, the following syntactic restrictions
(which are completely irrelevant) and which were only in place
for receivers are removed:
a) receiver types cannot be parenthesized
b) receiver parameter lists cannot have a trailing comma
The result of this CL is a simplication of the spec and the
implementation, with no impact on existing (or future) code.
Noteworthy:
- gc already permits a trailing comma at the end of a receiver
declaration:
func (recv T,) m() {}
This is technically a bug with the current spec; this CL will
legalize this notation.
- gccgo produces a misleading error when a trailing comma is used:
error: method has multiple receivers
(even though there's only one receiver)
- Compilers and type-checkers won't need to report errors anymore
if receiver types are parenthesized.
Fixes#4496.
LGTM=iant, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/101500044
Also made it extra clear for goto statements (even though label scopes
are already limited to the function defining a label).
Fixes#8040.
LGTM=r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/99550043
The spec was unclear about whether blank methods should be
permitted in interface types. gccgo permits at most one, gc
crashes if there are more than one, go/types permits at most
one.
Discussion:
Since method sets of non-interface types never contain methods
with blank names (blank methods are never declared), it is impossible
to satisfy an interface with a blank method.
It is possible to declare variables of assignable interface types
(but not necessarily identical types) containing blank methods, and
assign those variables to each other, but the values of those
variables can only be nil.
There appear to be two "reasonable" alternatives:
1) Permit at most one blank method (since method names must be unique),
and consider it part of the interface. This is what appears to happen
now, with corner-case bugs. Such interfaces can never be implemented.
2) Permit arbitrary many blank methods but ignore them. This appears
to be closer to the handling of blank identifiers in declarations.
However, an interface type literal is not a declaration (it's a type
literal). Also, for struct types, blank identifiers are not ignored;
so the analogy with declarations is flawed.
Both these alternatives don't seem to add any benefit and are likely
(if only slightly) more complicated to explain and implement than
disallowing blank methods in interfaces altogether.
Fixes#6604.
LGTM=r, rsc, iant
R=r, rsc, ken, iant
CC=golang-codereviews
https://golang.org/cl/99410046
The spec did not specify the order in which
init() functions are called. Specify that
they are called in source order since we have
now also specified the initialization order
of independent variables.
While technically a language change, no
existing code could have relied on this,
so this should not break anything.
Per suggestion from rsc.
LGTM=r, iant
R=rsc, iant, r, ken
CC=golang-codereviews
https://golang.org/cl/98420046
- split description of package initialization and
program execution
- better grouping of concerns in section on package
initialization
- more explicit definition of what constitues a
dependency
- removed language about constant dependencies -
they are computed at compile-time and not
initialized at run-time
- clarified that independent variables are initialized
in declaration order (rather than reference order)
Note that the last clarification is what distinguishes
gc and gccgo at the moment: gc uses reference order
(i.e., order in which variables are referenced in
initialization expressions), while gccgo uses declaration
order for independent variables.
Not a language change. But adopting this CL will
clarify what constitutes a dependency.
Fixes#6703.
LGTM=adonovan, r, iant, rsc
R=r, rsc, iant, ken, adonovan
CC=golang-codereviews
https://golang.org/cl/99020043
- use previously defined terms (with links) throughout
- specify evaluation order more precisely (in particular,
the evaluation time of rhs expressions in receive cases
was not specified)
- added extra example case
Not a language change.
Description matches observed behavior of code compiled
with gc and gccgo.
Fixes#7669.
LGTM=iant, r, rsc
R=r, rsc, iant, ken, josharian
CC=golang-codereviews
https://golang.org/cl/91230043
- A channel may be used between any number of goroutines,
not just two.
- Replace "passing a value" (which is not further defined)
by "sending and receiving a value".
- Made syntax production more symmetric.
- Talk about unbuffered channels before buffered channels.
- Clarify what the comma,ok receive values mean (issue 7785).
Not a language change.
Fixes#7785.
LGTM=rsc, r, iant
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/94030045
This is a clarification of what happens already.
Not a language change.
Fixes#7137.
LGTM=iant, r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/96000044
If the underlying type of a type T is a boolean, numeric,
or string type, then T is also a boolean, numeric, or
string type, respectively.
Not a language change.
Fixes#7551.
LGTM=iant, rsc, robert.hencke, r
R=r, rsc, iant, ken, robert.hencke
CC=golang-codereviews
https://golang.org/cl/100130044
Currently tip.golang.org leads to golang.org and
local godoc also leads to golang.org (when you don't have internet connectivity).
LGTM=crawshaw
R=golang-codereviews, crawshaw
CC=golang-codereviews
https://golang.org/cl/100200043
This documents the status quo for most implementations,
with one exception: gc generates a run-time error for
constant but out-of-range indices when slicing a constant
string. See issue 7200 for a detailed discussion.
LGTM=r
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/72160044
The underlying type of the predeclared type error is not itself,
but the interface it is defined as.
Fixes#7444.
LGTM=r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/71790044
This documents the implemented behavior of both
gc and gccgo as an implementation restriction.
NOT A LANGUAGE CHANGE.
Fixes#5425.
LGTM=rsc, r, iant
R=r, iant, rsc, ken
CC=golang-codereviews
https://golang.org/cl/71430043
gccgo considers built-in function calls returning a constant not as function call (issue 7386)
go/types considers any call (regular or built-in) as a function call
The wording and examples clarify that only "function calls" that are issued
at run-time (and thus do not result in a constant result) are considered
function calls in this case.
gc is inconsistent (issue 7385)
gccgo already interprets the spec accordingly and issue 7386 is moot.
go/types considers all calls (constant or not) as function calls (issue 7457).
Fixes#7387.
Fixes#7386.
LGTM=r, rsc, iant
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/66860046
An absent condition/tag in for and switch statements is equivalent
to the predeclared constant true; not simply the expression true
(which might lead to a locally defined true).
Not a language change.
Fixes#7404.
LGTM=iant, r
R=r, iant, rsc, ken
CC=golang-codereviews
https://golang.org/cl/68150046
No change to the meaning, just bad writing found by
Doug McIlroy.
Let's start the new year off with a bang.
R=golang-codereviews, bradfitz, dave
CC=golang-codereviews
https://golang.org/cl/47110044
Please note the slight rewording for append: The spec now
requires that append reuses the underlying array if it is
sufficiently large. Per majority sentiment.
This is technically a language change but the current
implementation always worked this way.
Fixes#5818.
Fixes#5180.
R=rsc, iant, r, ken, minux.ma, dan.kortschak, rogpeppe, go.peter.90
CC=golang-dev
https://golang.org/cl/14419054
