The example, var v, ok T1 = x.(T), can be interpreted as type T1 interface{} or type T = bool; type T1 = T.
Separating the example would help understanding for readers.
Change-Id: I179f4564e67f4d503815d29307df2cebb50c82f9
GitHub-Last-Rev: b34fffb6bb
GitHub-Pull-Request: golang/go#44040
Reviewed-on: https://go-review.googlesource.com/c/go/+/288472
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Robert Griesemer <gri@golang.org>
In the current (pre-CL) version of the spec, the 2nd last shift
example appears to be using the array declared in the last example.
On a 32-bit platform, that array would have length 0, which would
lead to a panic in the 2nd last example. Also, if this code were
inside a function, it wouldn't compile (array declared after use).
Use an explicitly declared array for that specific shift example.
Also, split out all cases that produce different results for 32-
vs 64-bit ints.
Fixes#41835.
Change-Id: Ie45114224509e4999197226f91f7f6f934449abb
Reviewed-on: https://go-review.googlesource.com/c/go/+/260398
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Suggested by @yaxinlx.
Fixes#41612.
Change-Id: I98b9968a95d090ee3c67ff02678e1874e6d98c33
Reviewed-on: https://go-review.googlesource.com/c/go/+/257159
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
The HTML linter 'tidy' reports:
go_spec.html:2556: Warning: unescaped & which should be written as &
go_spec.html:3293: Warning: unescaped & or unknown entity "&s1"
go_spec.html:3293: Warning: unescaped & or unknown entity "&a"
go_spec.html:3294: Warning: unescaped & or unknown entity "&s2"
go_spec.html:3294: Warning: unescaped & or unknown entity "&a"
go_spec.html:2045: Warning: trimming empty <p>
go_spec.html:4526: Warning: trimming empty <ul>
go_spec.html:4533: Warning: trimming empty <ul>
go_spec.html:4539: Warning: trimming empty <ul>
This CL fixes all but the <ul> ones, which I think should be fixed
but are defended by a comment.
Change-Id: I0ca88f5e80755024801877ab1298025ecf8f10c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/214457
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Since the word "regular" has a precise meaning in the context of
formal languages, the Introduction sentence claiming that Go's grammar
is "compact and regular" may mislead readers.
Reword it using Rob's suggestion.
Fixes#36037
Change-Id: I00c1a5714bdab8878d9a77b36d67dae67d63da0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/211277
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
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>
