- Rephrase the notion of "comparability" from a property
of values (operands) to a property of types and adjust
dependent prose.
- Introduce the notion of "strict comparability".
- Fix the definitions of comparability for type interfaces
and type parameters.
- Define the predeclared identifier "comparable" as stricly
comparable.
These changes address existing problems in the spec as outlined
in the section on "Related spec issues" in issue #56548.
For #56548.
Change-Id: Ibc8c2f36d92857a5134eadc18358624803d3dd21
Reviewed-on: https://go-review.googlesource.com/c/go/+/457095
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Document that a slice can be converted to either an array or a pointer
to an array of a matching underlying array type. This was documented in
the "Conversions from slice to array or array pointer" subsection, but
not in the list of conversion rules.
Updates #46505.
Change-Id: I16a89a63ef23c33580129952415e977a8f334009
Reviewed-on: https://go-review.googlesource.com/c/go/+/452936
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Tim King <taking@google.com>
If needed, the built-in function append allocates a new underlying
array. While we (probably) don't want to specify exactly how much
is allocated (the prose is deliberately vague), if there's more
space allocated than needed (cap > len after allocation), that
extra space is zeroed. Use an explicit link to the section on
Allocation which explicitly states that newly allocated memory
is zeroed.
Fixes#56684.
Change-Id: I9805d37c263b87860ea703ad143f738a0846247e
Reviewed-on: https://go-review.googlesource.com/c/go/+/452619
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
At parse time we don't know if a[i] is an index expression or a
type (or function) instantiation. Because instantiations accept
a list of type arguments, and argument lists permit a trailing
comma, a[i,] is either an instantiation or index expression.
Document that a trailing comma is permitted in the syntax for
index expressions.
For comparison, the same problem arises with conversions which
cannot be distinguished from function calls at parse time. The
spec also permits a trailing comma for conversions T(x,). The
grammar adjustment is the same (see line 5239).
Fixes#55007.
Change-Id: Ib9101efe52031589eb95a428cc6dff940d939f9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/452618
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
For #53003.
Change-Id: If5d76c7b8dfcbcab919cad9c333c0225fc155859
Reviewed-on: https://go-review.googlesource.com/c/go/+/449537
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Fixes#8606.
Change-Id: I64b13b2ed61ecae4641264deb47c9f7653a80356
Reviewed-on: https://go-review.googlesource.com/c/go/+/449536
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Converting from nil slice to zero element array is ok, so explicitly
describe the behavior in the spec.
For #46505
Change-Id: I68f432deb6c21a7549bf7e870185fc62504b37f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/430835
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
For #46505.
Change-Id: I1a30fd895496befd16626afb48717ac837ed5778
Reviewed-on: https://go-review.googlesource.com/c/go/+/429315
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
This permits a clear distinction between an individual assignment
and an assignment statement which may assign more than one value.
It also makes this section title consistent with all other section
titles about statements. Adjust internal links and prose where
appropriate. (Note that the spec already referred to assignment
statements in a couple of places, even before this change.)
Add an introductory paragraph to the section on assignment statements.
Preparation for adding a section on value vs reference types
(issue #5083).
Change-Id: Ie140ac296e653c67da2a5a203b63352b3dc4f9f5
Reviewed-on: https://go-review.googlesource.com/c/go/+/413615
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Pre-1.18, as special cases, the built-in operations append and copy
accepted strings as second arguments if the first argument was a byte
slice. With Go 1.18, these two built-ins as well as slice expressions
rely on the notion of core types in their specification.
Because we want to permit slice expressions, append, and copy to
operate on (1st or 2nd operands) that are type parameters restricted
by []byte | string (and variations thereof), the simple notion of
core type is not sufficient for these three operations. (The compiler
already permits such more relaxed operations).
In the section on core types, add a paragraph and examples introducing
the (artificial) core type "bypestring", which describes the core type
of type sets whose underlying types are []byte or string. Adjust the
rules for slice expressions, append, and copy accordingly.
Also (unrelated): Adjust prose in the only paragraph where we used
personal speech ("we") to impersonal speech, to match the rest of
the spec.
Fixes#52859.
Change-Id: I1cbda3095a1136fb99334cc3a62a9a349a27ce1e
Reviewed-on: https://go-review.googlesource.com/c/go/+/412234
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Add an additional example.
Fixes#53217.
Change-Id: I899376b9c1fa8dc5d475d8d3d6c8788ab79b0847
Reviewed-on: https://go-review.googlesource.com/c/go/+/412238
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
The spec section on conversions uses the terms "slice of bytes" and
"slice of runes". While not obviously clear, what is meant are slice
types whose element types are byte or rune types; specifically the
underlying types of the slices' element types must be byte or rune.
Some of this was evident from the examples, but not all of it. Made
this clearer by adding more examples illustrating various permitted
conversions.
Note that the 1.17 compiler did not accept the following conversions:
string([]myByte{...})
string([]myRune{...})
myString([]myByte{...})
myString([]myRune{...})
(where myByte, myRune, and myString have underlying types of byte,
rune, and string respectively) - it reported an internal error.
But it did accept the inverse conversions:
[]myByte("...")
[]myRune("...")
[]myByte(myString("..."))
[]myRune(myString("..."))
The 1.18 compiler made those conversions symmetric and they are now
permitted in both directions.
The extra examples reflect this reality.
Fixes#23814.
Change-Id: I5a1c200b45ddd0e8c0dc0d11da3a6c39cb2dc848
Reviewed-on: https://go-review.googlesource.com/c/go/+/412094
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
The spec already states that the precise behavior of the map size
hint provided to the make built-in is implementation-dependent.
Exclude requiring specific run-time behavior for maps.
(The current Go compiler does not panic if the size hint is negative
at run-time.)
Fixes#53219.
Change-Id: I2f3618bf9ba4ed921e18dc4f2273eaa770805bd7
Reviewed-on: https://go-review.googlesource.com/c/go/+/411919
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Types may be generic, so each occurrence of a TypeName may be
followed by optional type arguments. Add the missing syntactic
(EBNF) factor.
The syntax of type names followed by type arguments matches the
syntax of operand names followed by type arguments (operands may
also be types, or generic functions, among other things). This
opens the door to factoring out this shared syntax, but it will
also require some adjustments to prose to make it work well.
Leaving for another change.
Fixes#53240.
Change-Id: I15212225c28b27f7621e3ca80dfbd131f6b7eada
Reviewed-on: https://go-review.googlesource.com/c/go/+/411918
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
The types of embedded fields must be named, but they don't
need to be defined types (e.g. if the type name is an alias).
Fixes#41687.
Change-Id: Ib9de65dfab0e23c27d8303875fa45c217aa03331
Reviewed-on: https://go-review.googlesource.com/c/go/+/406054
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
The metasyntax used in the spec is exactly the Wirth Syntax
Notation (WSN), which eventually influenced EBNF. Add a link
but keep mentioning EBNF which is likely more commonly known.
Use the original terms in the productions. Specifically, use
the words "Term" and "Factor" rather than "Alternative" and
"Term".
The terminology cleanup also resolves an inconsistency in the
subsequent prose which is referring to the correct "terms" now.
While at it, add a production for the entire Syntax itself,
matching the original WSN definition.
Also, replace the two uses of "grammar" with "syntax" for
consistency ("syntax" is the prevalent term used throughout
the spec).
Fixes#50074.
Change-Id: If770d5f32f56f509f85893782c1dafbb0eb29b2e
Reviewed-on: https://go-review.googlesource.com/c/go/+/405814
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
- refer to character "categories" rather than "classes" per the
definitions in the Unicode standard
- use "uppercase", "lowercase" (one word) instead of "upper case"
or "upper-case", matching the spelling in the Unicode standard
- clarify that that the blank character "_" is considered a lowercase
letter for Go's purposes (export of identifiers)
Fixes#44715.
Change-Id: I54ef177d26c6c56624662fcdd6d1da60b9bb8d02
Reviewed-on: https://go-review.googlesource.com/c/go/+/405758
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Fixes#45652.
Change-Id: I5e1434480c12815369a6ce204f3729eb63139125
Reviewed-on: https://go-review.googlesource.com/c/go/+/405757
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Taking into account the discussion and relevant feedback on a
change proposed in 2013 (see e-mail thread mentioned in issue).
Fixes#48864.
Change-Id: I811d518b7cbdf6b815695174f1da3d4251f491c3
Reviewed-on: https://go-review.googlesource.com/c/go/+/405756
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Fixes#52628.
Change-Id: If4261abc25868d62f7689253d40f872692c23a4d
Reviewed-on: https://go-review.googlesource.com/c/go/+/405755
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Change scope rules per the accepted proposal #52038.
Match prose for type parameters of type declarations.
Fixing the implementation is tracked by #51503.
Fixes#52038.
For #51503.
Change-Id: Iebd88a82c896b7b2e8520cd514ef6a2cc903e807
Reviewed-on: https://go-review.googlesource.com/c/go/+/405754
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Be explicit that we always mean non-interface types when we
talk about sets of types.
Also, clarify that the quantification "all non-interface types"
means all such types in all possible programs, not just the
current program.
Per suggestion from Philip Wadler.
Change-Id: Ibc7b5823164e547bfcee85d4e523e58c7c27ac8a
Reviewed-on: https://go-review.googlesource.com/c/go/+/398655
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
In the Type identity section, the example provides various types as givens.
The example refers to the type *T5, but it is not provided in the givens.
I am assuming this was a typo, and was meant to refer to *A1 or *B1.
*B1 seems to be in alignment with the rest of the provided examples.
Change-Id: I554319ee8bca185c3643559321417e8b2a544ba0
GitHub-Last-Rev: e80560d32a
GitHub-Pull-Request: golang/go#52143
Reviewed-on: https://go-review.googlesource.com/c/go/+/398075
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Ian Lance Taylor <iant@golang.org>
Octal values over 255, like \400 or \777, are illegal. It wasn't clear if the expected behavior was a compile error, encoding the value as two characters, or if the value would be capped at 255.
This example explicitly shows that octal values over 255 are illegal.
Change-Id: I45d94680107029c5f083e5d434e6270cc5b258c1
GitHub-Last-Rev: f6bef0379f
GitHub-Pull-Request: golang/go#52111
Reviewed-on: https://go-review.googlesource.com/c/go/+/397555
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Be clear that the type of a term (not the term itself, which may
be of the form ~P) cannot be a type parameter.
For #50420.
Change-Id: I388d57be0618393d7ebe2c74ec04c1ebe3f33f7d
Reviewed-on: https://go-review.googlesource.com/c/go/+/396915
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
- Allow for a type parameter as length/capacity to make.
- Be slightly more precise in prose for append.
- Add a couple of links.
Change-Id: Ib97e528bab1ab55d271beeeb53d9bb7a07047b9b
Reviewed-on: https://go-review.googlesource.com/c/go/+/391754
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
- Remove "Draft" disclaimer. We're not done but the spec
is in usable shape with respect to generics features.
- Remove section on "Earlier version" and fold information
into the "Intro" section.
- Remove caveat for shifts: the rules for arithmetic operators
on type parameters apply for them as well.
- Simply state that we don't support arguments of type parameter
type for the built-ins real, imag, and complex.
Fixes#51182.
Change-Id: I6df1427de685cfe7055b64e91753aa7ebff70565
Reviewed-on: https://go-review.googlesource.com/c/go/+/391695
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
- Change section title from "Type parameters lists" to
"Type parameter declarations" as the enclosing section
is about declarations.
- Correct section on parsing ambiguity in type parameter
lists.
- Rephrase paragraphs on type parameters for method receivers
and adjust examples.
- Remove duplicate prose in section on function argument type
inference.
- Clarified "after substitution" column in Instantiations section.
Change-Id: Id76be9804ad96a3f1221e5c4942552dde015dfcb
Reviewed-on: https://go-review.googlesource.com/c/go/+/390994
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Specific types were introduced to explain rules for operands of
type parameter type. Specific types are really an implementation
mechanism to represent (possibly infinite) type sets in the machine;
they are not needed in the specification.
A specific type is either standing for a single named or unnamed
type, or it is the underlying (unnamed) type of an infinite set of
types. Each rule that applies to a type T of the set of specific
types must also apply to all types T' in the type set for which T
is a representative of. Thus, in the spec we can simply refer to
the type set directly, infinite or not.
Rather then excluding operands with empty type sets in each instance,
leave unspecified what happens when such an operand is used. Instead
give an implementation some leeway with an implementation restriction.
(The implementation restriction also needs to be formulated for types,
such as in conversions, which technically are not "operands". Left for
another CL.)
Minor: Remove the two uses of the word "concrete" to refer to non-
interface types; instead just say "non-interface type" for clarity.
Change-Id: I67ac89a640c995369c9d421a03820a0c0435835a
Reviewed-on: https://go-review.googlesource.com/c/go/+/390694
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Type inference for types was always a "nice to have" feature.
Given the under-appreciated complexity of making it work in all
cases, and the fact that we don't have a good understanding of
how it might affect readability of generic code, require explicit
type arguments for generic types.
This matches the current implementation.
Change-Id: Ie7ff6293d3fbea92ddc54c46285a4cabece7fe01
Reviewed-on: https://go-review.googlesource.com/c/go/+/390577
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
This change includes several smaller changes based on feedback
received so far.
These changes were reviewed at CL 385536. The only additional
change here is to the current date in the subtitle.
Change-Id: I653eb4a143e3b86c5357a2fd3b19168419c9f432
Reviewed-on: https://go-review.googlesource.com/c/go/+/390634
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
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Reviewed-by: Ian Lance Taylor <iant@golang.org>
The (temporary) highlights will make it easier to review the spec
in formatted form as opposed to html text.
Added a missing rule about the use of adjusted core types for
constraint type inference.
Adjusted rule for invalid embedding of interface types.
Change-Id: Ie573068d2307b66c937e803c486724175415b9c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/385535
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This change moves the relevant prose of the section on type parameters
into the section on type parameter lists and eliminates the former.
With this change, the section on types now exclusively describes all
Go composite types.
User-defined named types (defined types and type parameters) are
described with their declarations.
Change-Id: I3e421cd236e8801d31a4a81ff1e5ec9933e3ed20
Reviewed-on: https://go-review.googlesource.com/c/go/+/385037
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Also, fixed several closing header tags and removed a duplicate "the".
(Thanks to @hopehook and Hossein Zolfi for pointing these out.)
Change-Id: I85a40ba44b8570a578bce8d211dcc5ea3901fb1e
Reviewed-on: https://go-review.googlesource.com/c/go/+/385036
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
The outcome of type inference depends critically on when function
argument type inference stops processing arguments. Describe this
and explain an example with some detail.
Also: In the section on the built-in function delete, refer to the
value rather than the type of the second argument, as it may be an
untyped constant.
Change-Id: Ice7fbb33f985afe082380b8d37eaf763238a3818
Reviewed-on: https://go-review.googlesource.com/c/go/+/385034
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Change-Id: I6de236442f213ab4b4f19ec881add4923d8bfd8d
Reviewed-on: https://go-review.googlesource.com/c/go/+/385054
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Kevin Burke <kevin@burke.dev>
A basic interface is a classical Go interface containing only
methods or embedding basic interfaces.
Use this to simplify rule about what interfaces may be used
where. The term "basic interface" will also be useful when
talking about various interfaces in general.
Fix rule restricting union terms: as it was written it also
excluded interface terms with non-empty method sets due to
embedded non-interface types with methods.
Split the large section on interfaces into three smaller
pieces by introducing section titles.
Change-Id: I142a4d5609eb48aaa0f7800b5b85c1d6c0703fcb
Reviewed-on: https://go-review.googlesource.com/c/go/+/384994
Trust: Robert Griesemer <gri@golang.org>
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Reviewed-by: Ian Lance Taylor <iant@golang.org>
This makes the prose easier to read while being just as precise.
Change-Id: Ie46c6c5042f419de9fdeb1c75bb72b5a40c37073
Reviewed-on: https://go-review.googlesource.com/c/go/+/384774
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
This change only shuffles sections for better organization; there
are no other changes except title and link adjustments.
Until now, the sections on underlying types and method sets were
immediately following the introduction of types. As it becomes
necessary to introduce the notion of a core type more centrally,
the natural place is immediately following the section on underlying
types. All together, these sections, immediately after the introduction
of types, would distract from purpose of the section on types, which
is to introduce the various types that Go offers.
The more natural place for the definition of underlying, core, and
specific types is the section on properties of types and values.
To accomplish this, the section on the structure of interfaces is
split into a section on core types and one on specific types, and
the various sections are reorganized appropriately.
The new organization of the section on types now simply introduces
all Go types as follows:
- boolean types
- numeric types
- string types
- array types
- slice types
- struct types
- pointer types
- function types
- interface types
- map types
- channel types
- type parameters
The new organization of the section on properties of types and values
is as follows:
- underlying types
- core types
- specific types
- type identity
- assignability
- representability
- method sets
Change-Id: I59e4d47571da9d4c89d47d777f5353fb1c5843e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/384623
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Includes a few minor cosmetic changes.
Change-Id: I6c307d958b47d83671142688630ea7835168439f
Reviewed-on: https://go-review.googlesource.com/c/go/+/384622
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Fixes#51110.
Change-Id: I11370417f1ef435b05dfab18eeabc2c3c1b7b8a1
Reviewed-on: https://go-review.googlesource.com/c/go/+/384674
Trust: Robert Griesemer <gri@golang.org>
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Dan Scales <danscales@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Add corresponding rules and a couple of examples.
Fixes#50202.
Change-Id: I4287b5e2d0fd29a0c871795e07f1bb529c9c6004
Reviewed-on: https://go-review.googlesource.com/c/go/+/384240
Trust: Robert Griesemer <gri@golang.org>
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This change in terminology prevents potential confusion
that migth be caused by associating "structural type"
with "structural typing"; the two are not connected.
Also, adjusted introductory paragraph of section on
constraint type inference: type inference goes in both
directions, from type parameter to core type and vice
versa. The previous description was not quite accurate.
Change-Id: If4ca300f525eea660f68486302619aa6ad5dbc2c
Reviewed-on: https://go-review.googlesource.com/c/go/+/384238
Trust: Robert Griesemer <gri@golang.org>
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The terms "integer type", "floating-point type", and "complex type"
are used frequently in the spec but are not explicitly (only indirectly)
defined.
Slightly rephrased the section on numeric types and introduce these
terms explicitly. Add links to this section.
Change-Id: I3fb888933bece047da8b356b684c855618e9aee4
Reviewed-on: https://go-review.googlesource.com/c/go/+/384157
Trust: Robert Griesemer <gri@golang.org>
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Change-Id: Ic338788d6410ed0d09ad129811377ee9ce5ed496
Reviewed-on: https://go-review.googlesource.com/c/go/+/367954
Trust: Robert Griesemer <gri@golang.org>
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This reverts CL 380854.
Per the conluding discussions on #50791. A follow-up will
document `comparable` more thoroughly.
For #50791.
Change-Id: I15db9051784a012f713e28d725c3b8bbfeb40569
Reviewed-on: https://go-review.googlesource.com/c/go/+/381076
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Mostly from CL 367954.
Change-Id: Id003b0f785a286a1a649e4d6e8c87d0418a36545
Reviewed-on: https://go-review.googlesource.com/c/go/+/379920
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Introduce a (local) notion of a set of representative types,
which serves as a representation/approximation of an
interface's actual type set. If the set of representative
types is is non-empty and finite, it corresponds to the set
of specific types of the interface.
In the implementation, the set of representative types serves
as a finite representation of an interface's type set, together
with the set of methods.
Change-Id: Ib4c6cd5e17b81197672e4247be9737dd2cb6b56f
Reviewed-on: https://go-review.googlesource.com/c/go/+/376834
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Problem pointed out on golang-nuts mailing list.
Change-Id: If1c9b22e1ed7b4ec7ebcaadc80fa450333e6856c
Reviewed-on: https://go-review.googlesource.com/c/go/+/375799
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The new description matches the implementation (CL 370774).
Also, in the section on type constraints, use "defines" instead of
"determines" because the constraint interface defines the type set
which is precisely the set of acceptable type arguments.
For #49482.
Change-Id: I6f30f49100e8ba8bec0a0f1b450f88cae54312eb
Reviewed-on: https://go-review.googlesource.com/c/go/+/372874
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For #49602.
Change-Id: I0d3ff8f087dffb3409918494147fd1dceff7514d
Reviewed-on: https://go-review.googlesource.com/c/go/+/372694
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As written, the conversion P(x), where P and the type
of x are type parameters with identical underlying types
(i.e., identical constraints), is valid. However, unless
the type of x and P are identical (which is covered with
the assignability rule), such a conversion is not valid
in general (consider the case where both type parameters
are different type parameters with constraint "any").
This change adjusts the rules to prohibit type parameters
in this case. The same reasoning applies and the analogue
change is made for pointer types.
The type checker already implements these updated rules.
Change-Id: Id90187900cb2820f6a0a0cf582cf26cdf8addbce
Reviewed-on: https://go-review.googlesource.com/c/go/+/371074
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Change-Id: I562d4648756e710020ee491f3801896563a89baa
Reviewed-on: https://go-review.googlesource.com/c/go/+/367395
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We want to support some special cases for index expressions, len, and
cap on operands of type parameters (such as indexing a value constrained
by byte slices and strings), hence the extra rules.
Change-Id: I4a07dc7e64bb47361b021d606c52eae1784d5430
Reviewed-on: https://go-review.googlesource.com/c/go/+/366814
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Reviewed-by: Dan Scales <danscales@google.com>
- fix definition of "specific types" and add more examples
- state that a parameterized function must be instantiated
when used as a function value
- remove duplicate word ("can can" -> "can")
Thanks to @danscales for finding these.
Change-Id: Ideb41efc35a3e67694d3bc97e462454feae37c44
Reviewed-on: https://go-review.googlesource.com/c/go/+/367394
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Reviewed-by: Dan Scales <danscales@google.com>
This change corrects the link `Instantiantions` to `Instantiations` in the spec.
Change-Id: Ib0ed03420ae401d20af1ea723c5487018b2f462d
GitHub-Last-Rev: b84316c818
GitHub-Pull-Request: golang/go#49816
Reviewed-on: https://go-review.googlesource.com/c/go/+/367274
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Change-Id: I11111b3617673be94508128489aed6488d518537
Reviewed-on: https://go-review.googlesource.com/c/go/+/366834
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Change-Id: I5ffc7f26236487070447eaa0f6b14d1fab44c3c7
Reviewed-on: https://go-review.googlesource.com/c/go/+/366794
Trust: Robert Griesemer <gri@golang.org>
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Change-Id: I2770da87b4c977b51dfa046f2f08283917675e1c
Reviewed-on: https://go-review.googlesource.com/c/go/+/365916
Trust: Robert Griesemer <gri@golang.org>
Trust: Dan Scales <danscales@google.com>
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Reviewed-by: Dan Scales <danscales@google.com>
Change-Id: I7bfddf4be0d1d95419f312bb349ae2e16b74b795
Reviewed-on: https://go-review.googlesource.com/c/go/+/365915
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Change-Id: I3c4d8bdb5e92ee7fdca9593fb043f94f467755e8
Reviewed-on: https://go-review.googlesource.com/c/go/+/365434
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Change-Id: I4423a059527066c4418c195911f8184dfd3f5a15
Reviewed-on: https://go-review.googlesource.com/c/go/+/365914
Trust: Robert Griesemer <gri@golang.org>
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The notion of specific types will be used to define rules for
assignability, convertability, etc. when type parameters are
involved.
Change-Id: Ic5c134261e2a9fe05cdf25efd342f052458ab5c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/366754
Trust: Robert Griesemer <gri@golang.org>
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Thanks to @danscales for noticing the mistake.
Change-Id: I547ee80a78419765b82d39d7b34dc8d3bf962c35
Reviewed-on: https://go-review.googlesource.com/c/go/+/366215
Trust: Robert Griesemer <gri@golang.org>
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Reviewed-by: Dan Scales <danscales@google.com>
This change introduces the notion of a structural interface
and its corresponding structural type.
Change-Id: Ib5442dfd04cb5950b4467428cae51849f8922272
Reviewed-on: https://go-review.googlesource.com/c/go/+/365474
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- add section on type parameters
- added two sections on the scope of type parameters
- expanded general section on types accordingly
- introduced the notion of a named type which will
help in simplifying various rules (subsequent CLs)
Change-Id: I49c1ed7d6d4f951d751f0a3ca5dfb637e49829f2
Reviewed-on: https://go-review.googlesource.com/c/go/+/365414
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Change-Id: I29e9188a0fa1326c2755a9b86aeb47feaa8019be
Reviewed-on: https://go-review.googlesource.com/c/go/+/365274
Trust: Robert Griesemer <gri@golang.org>
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- fixed a typo in the method set section
- express in the syntax that ~T denotes an underlying type
- be more precise when talking about types vs type terms
- refer to "unions" rather than "union expressions"
- make it clear in the spec title that this is WIP
Change-Id: I9b2c4b1f77bc50dd574ed6893bedd40529c320fc
Reviewed-on: https://go-review.googlesource.com/c/go/+/365154
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This is the first of several CLs that update the existing
Go 1.17 spec for type parameters.
This CL updates the section on method sets and interface types.
It also adds "any", "comparable" to the list of predeclared
identifiers.
Change-Id: I0ce25dc02791c33150c0d949528512610faf3eab
Reviewed-on: https://go-review.googlesource.com/c/go/+/362999
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Thanks for jtagcat@ for finding this.
Change-Id: If7324808edbae19ec8bf503b04e0426f3fb3b47a
Reviewed-on: https://go-review.googlesource.com/c/go/+/363394
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Thanks to @bodar (Github) for finding this.
Fixes#48422.
Change-Id: I031c3d82a02db1d204e2b86b494d89784d37f073
Reviewed-on: https://go-review.googlesource.com/c/go/+/350409
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Reviewed-by: Matthew Dempsky <mdempsky@google.com>
CL 85215 added prose to provide some minimal intuition for the
definition of a "terminating statement". While the original definition
was perfectly fine, the added prose was actually incorrect: If the
terminating statement is a goto, it might jump to a labeled statement
following that goto in the same block (it could be the very next
statement), and thus a terminating statement does not in fact
"prevent execution of all statements that lexically appear after
it in the same block".
Rather than explaining the special case for gotos with targets that
are lexically following the goto in the same block, this CL opts for
a simpler approach.
Thanks to @3bodar (Github) for finding this.
Fixes#48323.
Change-Id: I8031346250341d038938a1ce6a75d3e687d32c37
Reviewed-on: https://go-review.googlesource.com/c/go/+/349172
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Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
So it's clear to the reader that if "M" is a promoted method from
embedded field "T", then "x.M" will be expanded to "x.T.M" during the
evaluation of the method value.
Fixes#47863
Change-Id: Id3b82127a2054584b6842c487f6e15c3102dc9fe
Reviewed-on: https://go-review.googlesource.com/c/go/+/344209
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There is an example for nil slice already, so adding example for non-nil
zero length slice, too, clarifying to the reader that the result is also
non-nil and different from nil slice case.
Updates #395
Change-Id: I019db1b1a1c0c621161ecaaacab5a4d888764b1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/336890
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For #19367
Change-Id: If0ff8ddba3b6b48e2e198cf3653e73284c7572a3
Reviewed-on: https://go-review.googlesource.com/c/go/+/332409
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Add unsafe.Add and unsafe.Slice to the list of built-in functions
which are not permitted in statement context. The compiler and
type checker already enforce this restriction, this just fixes
a documentation oversight.
For #19367.
For #40481.
Change-Id: Iabc63a8db048eaf40a5f5b5573fdf00b79d54119
Reviewed-on: https://go-review.googlesource.com/c/go/+/329925
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The word "specifier" is used once only here and technically not defined.
Change-Id: Ifc9f0582f4eb3c3011ba60d8008234de511d4be6
Reviewed-on: https://go-review.googlesource.com/c/go/+/323730
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Replace "reserved word" by "keyword" as the latter is the official term.
Change-Id: I9f269759b872026034a9f47e4a761cff2d348ca0
Reviewed-on: https://go-review.googlesource.com/c/go/+/323729
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1. The existing prose implied that a switch expression type must
be comparable because it is tested for equality against all case
expressions. But for an empty switch (no case expressions), it
was not clear if the switch expression needed to be comparable.
Require it to match the behavior of compiler and type checkers.
2. While making this change, remove redundant language explaining
what happens with untyped boolean switch expression values: the
default type of an untyped boolean value is bool, this is already
covered by the first part of the relevant sentence.
Fixes#43200.
Change-Id: Id8e0f29cfa8722b57cd2b7b58cba85b58c5f842b
Reviewed-on: https://go-review.googlesource.com/c/go/+/314411
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In Go1.13 and above, signed integers are permitted as shift counts as long as they are >=0.
However, the comments in the "Arithmetic operators" section says shift operators accept "unsigned integer" as of right operands. Replacing this with "integer>=0" resolves the misunderstanding that shift
operators permit only unsigned integers.
Reference: Go1.13 Release Notes: https://golang.org/doc/go1.13
Change-Id: Icd3c7734d539ab702590e992a618c9251c653c37
GitHub-Last-Rev: 4f263a48d3
GitHub-Pull-Request: golang/go#44664
Reviewed-on: https://go-review.googlesource.com/c/go/+/297249
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Trust: Robert Griesemer <gri@golang.org>
