Delimiter in proc_macro - Rust (original) (raw)

Enum Delimiter

1.29.0 · Source

pub enum Delimiter {
    Parenthesis,
    Brace,
    Bracket,
    None,
}

Expand description

Describes how a sequence of token trees is delimited.

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( ... )

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{ ... }

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[ ... ]

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∅ ... ∅An invisible delimiter, that may, for example, appear around tokens coming from a “macro variable” $var. It is important to preserve operator priorities in cases like$var * 3 where $var is 1 + 2. Invisible delimiters might not survive roundtrip of a token stream through a string.

Note: rustc currently can ignore the grouping of tokens delimited by None in the output of a proc_macro. Only None-delimited groups created by a macro_rules macro in the input of a proc_macro macro are preserved, and only in very specific circumstances. Any None-delimited groups (re)created by a proc_macro will therefore not preserve operator priorities as indicated above. The other Delimiter variants should be used instead in this context. This is a rustc bug. For details, seerust-lang/rust#67062.

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Tests for self and other values to be equal, and is used by ==.

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Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

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