61 lines
1.9 KiB
Markdown
61 lines
1.9 KiB
Markdown
Variables
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=========
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{{#include ../links.md}}
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Valid Names
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-----------
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Variables in Rhai follow normal C naming rules - must contain only ASCII letters, digits and underscores '`_`',
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and cannot start with a digit.
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For example: '`_c3po`' and '`r2d2`' are valid variable names, but '`3abc`' is not.
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However, unlike Rust, a variable name must also contain at least one ASCII letter, and an ASCII letter must come before any digit.
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In other words, the first character that is not an underscore '`_`' must be an ASCII letter and not a digit.
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Therefore, some names acceptable to Rust, like '`_`', '`_42foo`', '`_1`' etc., are not valid in Rhai.
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This restriction is to reduce confusion because, for instance, '`_1`' can easily be misread (or mis-typed) as `-1`.
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Variable names are case _sensitive_.
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Variable names also cannot be the same as a [keyword].
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### Unicode Standard Annex #31 Identifiers
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The [`unicode-xid-ident`] feature expands the allowed characters for variable names to the set defined by
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[Unicode Standard Annex #31](http://www.unicode.org/reports/tr31/).
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Declare a Variable
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------------------
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Variables are declared using the `let` keyword.
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Variables do not have to be given an initial value.
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If none is provided, it defaults to [`()`].
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A variable defined within a statement block is _local_ to that block.
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```rust
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let x; // ok - value is '()'
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let x = 3; // ok
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let _x = 42; // ok
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let x_ = 42; // also ok
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let _x_ = 42; // still ok
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let _ = 123; // <- syntax error: illegal variable name
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let _9 = 9; // <- syntax error: illegal variable name
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let x = 42; // variable is 'x', lower case
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let X = 123; // variable is 'X', upper case
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x == 42;
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X == 123;
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{
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let x = 999; // local variable 'x' shadows the 'x' in parent block
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x == 999; // access to local 'x'
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}
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x == 42; // the parent block's 'x' is not changed
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```
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