45 lines
1.1 KiB
Markdown
45 lines
1.1 KiB
Markdown
Constants
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=========
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Constants can be defined using the `const` keyword and are immutable.
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```rust
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const X; // 'X' is a constant '()'
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const X = 40 + 2; // 'X' is a constant 42
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print(X * 2); // prints 84
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X = 123; // <- syntax error: constant modified
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```
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```admonish tip.small "Tip: Naming"
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Constants follow the same naming rules as [variables](variables.md),
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but as a convention are often named with all-capital letters.
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```
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Automatic Global Module
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-----------------------
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When a [constant](constants.md) is declared at global scope, it is added to a special
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[module](modules/index.md) called `global`.
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[Functions](functions.md) can access those [constants](constants.md) via the special `global`
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[module](modules/index.md).
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```rust
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const CONSTANT = 42; // this constant is automatically added to 'global'
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{
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const INNER = 0; // this constant is not at global level
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} // <- it goes away here
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fn foo(x) {
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x *= global::CONSTANT; // ok! 'CONSTANT' exists in 'global'
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x * global::INNER // <- error: constant 'INNER' not found in 'global'
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}
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```
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