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>
TryBot-Result: Gopher Robot <gobot@golang.org>
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>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
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>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Change-Id: Ic338788d6410ed0d09ad129811377ee9ce5ed496
Reviewed-on: https://go-review.googlesource.com/c/go/+/367954
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Mostly from CL 367954.
Change-Id: Id003b0f785a286a1a649e4d6e8c87d0418a36545
Reviewed-on: https://go-review.googlesource.com/c/go/+/379920
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
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
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Problem pointed out on golang-nuts mailing list.
Change-Id: If1c9b22e1ed7b4ec7ebcaadc80fa450333e6856c
Reviewed-on: https://go-review.googlesource.com/c/go/+/375799
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
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
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>
For #49602.
Change-Id: I0d3ff8f087dffb3409918494147fd1dceff7514d
Reviewed-on: https://go-review.googlesource.com/c/go/+/372694
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>
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
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
