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Propose the decision from #542, noting implementation from #563 Also integrates some of #339 into `variables.md` because that's actually how this started, looking for a proposal reference for #542 Co-authored-by: Richard Smith <richard@metafoo.co.uk> Co-authored-by: josh11b <josh11b@users.noreply.github.com>
66 lines
1.7 KiB
Markdown
66 lines
1.7 KiB
Markdown
# Variables
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Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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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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## Table of contents
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- [Overview](#overview)
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- [Notes](#notes)
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- [Alternatives](#alternatives)
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- [Global variables](#global-variables)
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- [Relevant proposals](#relevant-proposals)
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## Overview
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Carbon's local variable syntax is:
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> `var` _identifier_`:` _type_ _[_ `=` _value_ _]_`;`
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Blocks introduce nested scopes and can contain local variable declarations that
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work similarly to function parameters.
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For example:
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```
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fn Foo() {
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var x: Int = 42;
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}
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```
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This introduces a local variable named `x` into the block's scope. It has the
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type `Int` and is initialized with the value `42`. These variable declarations
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(and function declarations) have a lot more power than what we're covering just
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yet, but this gives you the basic idea.
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While there can be global constants, there are no global variables.
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## Notes
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> TODO: Constant syntax is an ongoing discussion.
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## Alternatives
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### Global variables
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We are exploring several different ideas for how to design less bug-prone
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patterns to replace the important use cases programmers still have for global
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variables. We may be unable to fully address them, at least for migrated code,
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and be forced to add some limited form of global variables back. We may also
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discover that their convenience outweighs any improvements afforded.
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## Relevant proposals
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Most discussion of design choices and alternatives may be found in relevant
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proposals.
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- [`var` statement](/proposals/p0339.md)
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- [`var` ordering](/proposals/p0618.md)
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