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Mark what is provisional in the design overview (#1984)
Also references were added to clarify that some features are not provisional. Co-authored-by: Jon Ross-Perkins <jperkins@google.com> Co-authored-by: Geoff Romer <gromer@google.com>
This commit is contained in:
josh11b
co-authored by
Jon Ross-Perkins
Geoff Romer
Jon Ross-Perkins
Geoff Romer
parent
bb0aac61a3
commit
09e4417431
+123
-16
@@ -6,6 +6,9 @@ Exceptions. See /LICENSE for license information.
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SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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-->
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> **STATUS:** Up-to-date on 09-Aug-2022, including proposals up through
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> [#1327](https://github.com/carbon-language/carbon-lang/pull/1327).
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<!-- toc -->
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## Table of contents
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@@ -134,6 +137,7 @@ This document includes much that is provisional or placeholder. This means that
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the syntax used, language rules, standard library, and other aspects of the
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design have things that have not been decided through the Carbon process. This
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preliminary material fills in gaps until aspects of the design can be filled in.
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Features that are provisional have been marked as such on a best-effort basis.
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## Hello, Carbon
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@@ -347,6 +351,9 @@ selected.
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### String types
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> **Note:** This is provisional, no design for string types has been through the
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> proposal process yet.
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There are two string types:
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- `String` - a byte sequence treated as containing UTF-8 encoded text.
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@@ -390,9 +397,6 @@ are available for representing strings with `\`s and `"`s.
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## Value categories and value phases
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**FIXME:** Should this be moved together with
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[Types are values](#types-are-values)?
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Every value has a
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[value category](<https://en.wikipedia.org/wiki/Value_(computer_science)#lrvalue>),
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similar to [C++](https://en.cppreference.com/w/cpp/language/value_category),
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@@ -435,6 +439,10 @@ generally convert into runtime values if an operation that inspects the value is
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performed on them. Runtime values will convert into constants or to symbolic
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values if constant evaluation of the runtime expression succeeds.
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> **Note:** Conversion of runtime values to other phases is provisional, as are
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> the semantics of r-values. See pending proposal
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> [#821: Values, variables, pointers, and references](https://github.com/carbon-language/carbon-lang/pull/821).
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## Composite types
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### Tuples
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@@ -471,6 +479,10 @@ fn DoubleTuple(x: (i32, i32)) -> (i32, i32) {
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Tuple types are
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[structural](https://en.wikipedia.org/wiki/Structural_type_system).
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> **Note:** This is provisional, no design for tuples has been through the
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> proposal process yet. Many of these questions were discussed in dropped
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> proposal [#111](https://github.com/carbon-language/carbon-lang/pull/111).
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> References: [Tuples](tuples.md)
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### Struct types
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@@ -521,6 +533,10 @@ type `Optional(T*)`.
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[stricter pointer provenance](https://www.ralfj.de/blog/2022/04/11/provenance-exposed.html)
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or restrictions on casts between pointers and integers.
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> **Note:** While the syntax for pointers has been decided, the semantics of
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> pointers are provisional, as is the syntax for optionals. See pending proposal
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> [#821: Values, variables, pointers, and references](https://github.com/carbon-language/carbon-lang/pull/821).
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> References:
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>
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> - Question-for-leads issue
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@@ -552,6 +568,10 @@ Console.Print(a[0]);
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> **TODO:** Slices
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> **Note:** This is provisional, no design for arrays has been through the
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> proposal process yet. See pending proposal
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> [#1928: Arrays](https://github.com/carbon-language/carbon-lang/pull/1928).
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## Expressions
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Expressions describe some computed value. The simplest example would be a
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@@ -654,6 +674,9 @@ function or class itself is visible until the end of the enclosing scope.
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## Patterns
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> **Note:** This is provisional, no design for patterns has been through the
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> proposal process yet.
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A _pattern_ says how to receive some data that is being matched against. There
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are two kinds of patterns:
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@@ -782,6 +805,9 @@ Here `x: i64` is the pattern, which is followed by an equal sign (`=`) and the
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value to match, `42`. The names from [binding patterns](#binding-patterns) are
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introduced into the enclosing [scope](#declarations-definitions-and-scopes).
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> **Note:** `let` declarations are provisional. See pending proposal
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> [#821: Values, variables, pointers, and references](https://github.com/carbon-language/carbon-lang/pull/821).
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### Variable `var` declarations
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A `var` declaration is similar, except with `var` bindings, so `x` here is an
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@@ -897,6 +923,10 @@ the caller, and dereferencing using `*` in the callee.
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Outputs of a function should prefer to be returned. Multiple values may be
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returned using a [tuple](#tuples) or [struct](#struct-types) type.
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> **Note:** The semantics of parameter passing are provisional. See pending
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> proposal
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> [#821: Values, variables, pointers, and references](https://github.com/carbon-language/carbon-lang/pull/821).
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### `auto` return type
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If `auto` is used in place of the return type, the return type of the function
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@@ -967,6 +997,9 @@ the assignment.
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Unlike C++, these assignments are statements, not expressions, and don't return
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a value.
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> **Note:** The semantics of assignment are provisional. See pending proposal
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> [#821: Values, variables, pointers, and references](https://github.com/carbon-language/carbon-lang/pull/821).
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### Control flow
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Blocks of statements are generally executed sequentially. Control-flow
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@@ -1093,7 +1126,13 @@ for (var step: Step in steps) {
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}
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```
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> References: [`break`](control_flow/loops.md#break)
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> References:
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>
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> - [`break`](control_flow/loops.md#break)
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> - Proposal
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> [#340: Add C++-like `while` loops](https://github.com/carbon-language/carbon-lang/pull/340)
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> - Proposal
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> [#353: Add C++-like `for` loops](https://github.com/carbon-language/carbon-lang/pull/353)
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##### `continue`
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@@ -1113,7 +1152,13 @@ while (!f.EOF()) {
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}
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```
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> References: [`continue`](control_flow/loops.md#continue)
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> References:
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>
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> - [`continue`](control_flow/loops.md#continue)
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> - Proposal
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> [#340: Add C++-like `while` loops](https://github.com/carbon-language/carbon-lang/pull/340)
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> - Proposal
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> [#353: Add C++-like `for` loops](https://github.com/carbon-language/carbon-lang/pull/353)
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#### `return`
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@@ -1223,6 +1268,9 @@ fn Foo() -> f32 {
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}
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```
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> **Note:** This is provisional, no design for `match` statements has been
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> through the proposal process yet.
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> References:
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>
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> - [Pattern matching](pattern_matching.md)
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@@ -1231,8 +1279,6 @@ fn Foo() -> f32 {
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## User-defined types
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> **TODO:** Maybe rename to "nominal types"?
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### Classes
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_Nominal classes_, or just
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@@ -1316,7 +1362,9 @@ sprocket = {.x = 2, .y = 1, .payload = "Bounce"};
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> References:
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>
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> - [Classes: Construction](classes.md#construction)
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> - [Classes: Assignment](classes.md#assignment)
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> - Proposal
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> [#722: Nominal classes and methods](https://github.com/carbon-language/carbon-lang/pull/722)
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> - Proposal
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> [#981: Implicit conversions for aggregates](https://github.com/carbon-language/carbon-lang/pull/981)
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@@ -1364,6 +1412,12 @@ class Registered {
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This approach can also be used for types that can't be copied or moved.
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> References:
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>
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> - [Classes: Construction](classes.md#construction)
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> - Proposal
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> [#722: Nominal classes and methods](https://github.com/carbon-language/carbon-lang/pull/722)
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#### Methods
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Class type definitions can include methods:
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@@ -1522,7 +1576,7 @@ class DerivedFromAbstract extends AbstractClass {
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> References:
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>
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> - [Inheritance](classes.md#inheritance)
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> - [Classes: Inheritance](classes.md#inheritance)
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> - Proposal
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> [#777: Inheritance](https://github.com/carbon-language/carbon-lang/pull/777)
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> - Proposal
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@@ -1546,6 +1600,8 @@ names resolvable by the compiler, and don't act like forward declarations.
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> - [Access control for class members](classes.md#access-control)
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> - Question-for-leads issue
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> [#665: `private` vs `public` _syntax_ strategy, as well as other visibility tools like `external`/`api`/etc.](https://github.com/carbon-language/carbon-lang/issues/665)
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> - Proposal
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> [#777: Inheritance](https://github.com/carbon-language/carbon-lang/pull/777)
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> - Question-for-leads issue
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> [#971: Private interfaces in public API files](https://github.com/carbon-language/carbon-lang/issues/971)
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@@ -1585,14 +1641,14 @@ type, use `UnsafeDelete`.
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> References:
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>
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> - [Destructors](classes.md#destructors)
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> - [Classes: Destructors](classes.md#destructors)
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> - Proposal
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> [#1154: Destructors](https://github.com/carbon-language/carbon-lang/pull/1154)
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#### `const`
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**Note:** This is provisional, no design for `const` has been through the
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proposal process yet.
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> **Note:** This is provisional, no design for `const` has been through the
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> proposal process yet.
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For every type `MyClass`, there is the type `const MyClass` such that:
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@@ -1672,6 +1728,12 @@ when returning a value from a function or by using the _move operator_ `~x`.
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This leaves `x` in an [unformed state](#unformed-state) and returns its old
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value.
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> **Note:** This is provisional. The move operator was discussed but not
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> proposed in accepted proposal
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> [#257: Initialization of memory and variables](https://github.com/carbon-language/carbon-lang/pull/257).
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> See pending proposal
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> [#821: Values, variables, pointers, and references](https://github.com/carbon-language/carbon-lang/pull/821).
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#### Mixins
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Mixins allow reuse with different trade-offs compared to
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@@ -1681,7 +1743,9 @@ be done using
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[multiple inheritance](https://en.wikipedia.org/wiki/Multiple_inheritance) in
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C++.
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**TODO:** The design for mixins is still under development.
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> **TODO:** The design for mixins is still under development. The details here
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> are provisional. The mixin use case was included in accepted proposal
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> [#561: Basic classes: use cases, struct literals, struct types, and future work](https://github.com/carbon-language/carbon-lang/pull/561).
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### Choice types
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@@ -1921,7 +1985,7 @@ given name public.
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### Package scope
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The top-level scope in a package is the scope of the package. This means:
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The top-level scope in a file is the scope of the package. This means:
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- Within this scope (and its sub-namespaces), all visible names from the same
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package appear. This includes names from the same file, names from the `api`
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@@ -2036,6 +2100,12 @@ P.M.Q();
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>
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> - ["Namespaces" in "Code and name organization"](code_and_name_organization/README.md#namespaces)
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> - ["Package and namespace members" in "Qualified names and member access"](expressions/member_access.md#package-and-namespace-members)
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> - Proposal
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> [#107: Code and name organization](https://github.com/carbon-language/carbon-lang/pull/107)
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> - Proposal
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> [#989: Member access expressions](https://github.com/carbon-language/carbon-lang/pull/989)
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> - Question-for-leads issue
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> [#1136: what is the top-level scope in a source file, and what names are found there?](https://github.com/carbon-language/carbon-lang/issues/1136)
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### Naming conventions
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@@ -2106,9 +2176,13 @@ class ContactInfo {
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> - [`alias` a name from an external impl](generics/details.md#external-impl)
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> - [`alias` a name in a named constraint](generics/details.md#named-constraints)
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> - Proposal
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> [#107: Code and name organization](https://github.com/carbon-language/carbon-lang/pull/107)
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> - Proposal
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> [#553: Generics details part 1](https://github.com/carbon-language/carbon-lang/pull/553)
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> - Question-for-leads issue
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> [#749: Alias syntax](https://github.com/carbon-language/carbon-lang/issues/749)
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> - Proposal
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> [#989: Member access expressions](https://github.com/carbon-language/carbon-lang/pull/989)
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### Name lookup
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@@ -2593,6 +2667,10 @@ indicate that they may not be specialized, subject to
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> [#920: Generic parameterized impls (details 5)](https://github.com/carbon-language/carbon-lang/pull/920)
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> - Proposal
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> [#983: Generics details 7: final impls](https://github.com/carbon-language/carbon-lang/pull/983)
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> - Question-for-leads issue
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> [1192: Parameterized impl syntax](https://github.com/carbon-language/carbon-lang/issues/1192)
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> - Proposal
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> [#1327: Generics: `impl forall`](https://github.com/carbon-language/carbon-lang/pull/1327)
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### Other features
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@@ -2620,9 +2698,9 @@ Carbon generics have a number of other features, including:
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value with a type implementing an interface, and allows the functions in
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that interface to be called using
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[dynamic dispatch](https://en.wikipedia.org/wiki/Dynamic_dispatch), for some
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interfaces marked "`dyn`-safe".
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interfaces marked "`dyn`-safe". **Note:** Provisional.
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- [Variadics](generics/details.md#variadic-arguments) supports variable-length
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parameter lists.
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parameter lists. **Note:** Provisional.
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> References:
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>
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@@ -2883,6 +2961,9 @@ include:
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### Importing and `#include`
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> **Note:** This is provisional, no design for importing C++ has been through
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> the proposal process yet.
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A C++ library header file may be [imported](#imports) into Carbon using an
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`import` declaration of the special `Cpp` package.
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@@ -2919,6 +3000,9 @@ marker.
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### ABI and dynamic linking
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> **Note:** This reflects goals and plans. No specific design for the
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> implementation has been through the proposal process yet.
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Carbon itself will not have a stable ABI for the language as a whole, and most
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language features will be designed around not having any ABI stability. Instead,
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we expect to add dedicated language features that are specifically designed to
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@@ -2943,8 +3027,16 @@ available across this interop boundary will of course be restricted to what is
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expressible in the C ABI, and types may need explicit markers to have guaranteed
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ABI compatibility.
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> References:
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>
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> - [Goals: Stable language and library ABI non-goal](https://github.com/carbon-language/carbon-lang/blob/trunk/docs/project/goals.md#stable-language-and-library-abi)
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> - [#175: C++ interoperability goals: Support mixing Carbon and C++ toolchains](/proposals/p0175.md#support-mixing-carbon-and-c-toolchains)
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### Operator overloading
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> **Note:** This is provisional, no design for this has been through the
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> proposal process yet.
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[Operator overloading](#operator-overloading) is supported in Carbon, but is
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done by [implementing an interface](#interfaces-and-implementations) instead of
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defining a method or nonmember function as in C++.
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@@ -2984,6 +3076,9 @@ requiring changes to importers?
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### Templates
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> **Note:** This is provisional, no design for this has been through the
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> proposal process yet.
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Carbon supports both
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[checked and template generics](#checked-and-template-parameters). This provides
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a migration path for C++ template code:
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@@ -3012,6 +3107,9 @@ if it were a C++ template.
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### Standard types
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> **Note:** This is provisional, no design for this has been through the
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> proposal process yet.
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The Carbon integer types, like `i32` and `u64`, are considered equal to the
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corresponding fixed-width integer types in C++, like `int32_t` and `uint64_t`,
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provided by `<stdint.h>` or `<cstdint>`. The basic C and C++ integer types like
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@@ -3076,12 +3174,21 @@ The reverse operation is also possible using a proxy object implementing a C++
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abstract base class and holding a pointer to a type implementing the
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corresponding interface.
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> References:
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>
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> - Proposal
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> [#561: Basic classes: use cases, struct literals, struct types, and future work](https://github.com/carbon-language/carbon-lang/pull/561)
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> - Proposal
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> [#777: Inheritance](https://github.com/carbon-language/carbon-lang/pull/777)
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### Enums
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> **TODO**
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## Unfinished tales
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> **Note:** Everything in this section is provisional and forward looking.
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### Safety
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Carbon's premise is that C++ users can't give up performance to get safety. Even
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Reference in New Issue
Block a user