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<!DOCTYPE html> < html lang = "en" > < head > < meta charset = "utf-8" > < meta name = "viewport" content = "width=device-width, initial-scale=1.0" > < meta name = "generator" content = "rustdoc" > < meta name = "description" content = "Generate a flags type." > < title > bitflags in bitflags - Rust< / title > < script > if ( window . location . protocol !== "file:" ) document . head . insertAdjacentHTML ( "beforeend" , "SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2" . split ( "," ) . map ( f => ` <link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/ ${ f } "> ` ) . join ( "" ) ) < / script > < link rel = "stylesheet" href = "../static.files/normalize-76eba96aa4d2e634.css" > < link rel = "stylesheet" href = "../static.files/rustdoc-dd39b87e5fcfba68.css" > < meta name = "rustdoc-vars" data-root-path = "../" data-static-root-path = "../static.files/" data-current-crate = "bitflags" data-themes = "" data-resource-suffix = "" data-rustdoc-version = "1.80.0 (051478957 2024-07-21)" data-channel = "1.80.0" data-search-js = "search-d52510db62a78183.js" data-settings-js = "settings-4313503d2e1961c2.js" > < script src = "../static.files/storage-118b08c4c78b968e.js" > < / script > < script defer src = "sidebar-items.js" > < / script > < script defer src = "../static.files/main-20a3ad099b048cf2.js" > < / script > < noscript > < link rel = "stylesheet" href = "../static.files/noscript-df360f571f6edeae.css" > < / noscript > < link rel = "alternate icon" type = "image/png" href = "../static.files/favicon-32x32-422f7d1d52889060.png" > < link rel = "icon" type = "image/svg+xml" href = "../static.files/favicon-2c020d218678b618.svg" > < / head > < body class = "rustdoc macro" > <!-- [if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif] --> < nav class = "mobile-topbar" > < button class = "sidebar-menu-toggle" title = "show sidebar" > < / button > < / nav > < nav class = "sidebar" > < div class = "sidebar-crate" > < h2 > < a href = "../bitflags/index.html" > bitflags< / a > < span class = "version" > 2.6.0< / span > < / h2 > < / div > < div class = "sidebar-elems" > < / div > < / nav > < div class = "sidebar-resizer" > < / div > < main > < div class = "width-limiter" > < rustdoc-search > < / rustdoc-search > < section id = "main-content" class = "content" > < div class = "main-heading" > < h1 > Macro < a href = "index.html" > bitflags< / a > ::< wbr > < a class = "macro" href = "#" > bitflags< / a > < button id = "copy-path" title = "Copy item path to clipboard" > Copy item path< / button > < / h1 > < span class = "out-of-band" > < a class = "src" href = "../src/bitflags/lib.rs.html#447-588" > source< / a > · < button id = "toggle-all-docs" title = "collapse all docs" > [< span > − < / span > ]< / button > < / span > < / div > < pre class = "rust item-decl" > < span class = "macro" > macro_rules!< / span > bitflags {
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(
$(< span class = "attr" > #[< span class = "macro-nonterminal" > $outer< / span > :meta]< / span > )*
< span class = "macro-nonterminal" > $vis< / span > :vis < span class = "kw" > struct < / span > < span class = "macro-nonterminal" > $BitFlags< / span > :ident: < span class = "macro-nonterminal" > $T< / span > :ty {
$(
$(< span class = "attr" > #[< span class = "macro-nonterminal" > $inner< / span > :ident $(< span class = "macro-nonterminal" > $args< / span > :tt)< span class = "kw-2" > *< / span > ]< / span > )*
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< span class = "kw" > const < / span > < span class = "macro-nonterminal" > $Flag< / span > :tt = < span class = "macro-nonterminal" > $value< / span > :expr;
)*
}
$(< span class = "macro-nonterminal" > $t< / span > :tt)*
) => { ... };
(
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$(< span class = "attr" > #[< span class = "macro-nonterminal" > $outer< / span > :meta]< / span > )*
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< span class = "kw" > impl < / span > < span class = "macro-nonterminal" > $BitFlags< / span > :ident: < span class = "macro-nonterminal" > $T< / span > :ty {
$(
$(< span class = "attr" > #[< span class = "macro-nonterminal" > $inner< / span > :ident $(< span class = "macro-nonterminal" > $args< / span > :tt)< span class = "kw-2" > *< / span > ]< / span > )*
< span class = "kw" > const < / span > < span class = "macro-nonterminal" > $Flag< / span > :tt = < span class = "macro-nonterminal" > $value< / span > :expr;
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)*
}
$(< span class = "macro-nonterminal" > $t< / span > :tt)*
) => { ... };
() => { ... };
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}< / pre > < details class = "toggle top-doc" open > < summary class = "hideme" > < span > Expand description< / span > < / summary > < div class = "docblock" > < p > Generate a flags type.< / p >
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< h2 id = "struct-mode" > < a class = "doc-anchor" href = "#struct-mode" > §< / a > < code > struct< / code > mode< / h2 >
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< p > A declaration that begins with < code > $vis struct< / code > will generate a < code > struct< / code > for a flags type, along with
methods and trait implementations for it. The body of the declaration defines flags as constants,
where each constant is a flags value of the generated flags type.< / p >
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< h3 id = "examples" > < a class = "doc-anchor" href = "#examples" > §< / a > Examples< / h3 >
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< p > Generate a flags type using < code > u8< / code > as the bits type:< / p >
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< div class = "example-wrap" > < pre class = "rust rust-example-rendered" > < code > < span class = "macro" > bitflags!< / span > {
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< span class = "kw" > struct < / span > Flags: u8 {
< span class = "kw" > const < / span > A = < span class = "number" > 1< / span > ;
< span class = "kw" > const < / span > B = < span class = "number" > 1 < / span > < < < span class = "number" > 1< / span > ;
< span class = "kw" > const < / span > C = < span class = "number" > 0b0000_0100< / span > ;
}
}< / code > < / pre > < / div >
< p > Flags types are private by default and accept standard visibility modifiers. Flags themselves
are always public:< / p >
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< div class = "example-wrap" > < pre class = "rust rust-example-rendered" > < code > < span class = "macro" > bitflags!< / span > {
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< span class = "kw" > pub struct < / span > Flags: u8 {
< span class = "comment" > // Constants are always `pub`
< / span > < span class = "kw" > const < / span > A = < span class = "number" > 1< / span > ;
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}
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}< / code > < / pre > < / div >
< p > Flags may refer to other flags using their < a href = "trait.Flags.html#tymethod.bits" title = "method bitflags::Flags::bits" > < code > Flags::bits< / code > < / a > value:< / p >
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< div class = "example-wrap" > < pre class = "rust rust-example-rendered" > < code > < span class = "macro" > bitflags!< / span > {
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< span class = "kw" > struct < / span > Flags: u8 {
< span class = "kw" > const < / span > A = < span class = "number" > 1< / span > ;
< span class = "kw" > const < / span > B = < span class = "number" > 1 < / span > < < < span class = "number" > 1< / span > ;
< span class = "kw" > const < / span > AB = Flags::A.bits() | Flags::B.bits();
}
}< / code > < / pre > < / div >
< p > A single < code > bitflags< / code > invocation may include zero or more flags type declarations:< / p >
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< div class = "example-wrap" > < pre class = "rust rust-example-rendered" > < code > < span class = "macro" > bitflags!< / span > {}
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< span class = "macro" > bitflags!< / span > {
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< span class = "kw" > struct < / span > Flags1: u8 {
< span class = "kw" > const < / span > A = < span class = "number" > 1< / span > ;
}
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< span class = "kw" > struct < / span > Flags2: u8 {
< span class = "kw" > const < / span > A = < span class = "number" > 1< / span > ;
}
}< / code > < / pre > < / div >
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< h2 id = "impl-mode" > < a class = "doc-anchor" href = "#impl-mode" > §< / a > < code > impl< / code > mode< / h2 >
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< p > A declaration that begins with < code > impl< / code > will only generate methods and trait implementations for the
< code > struct< / code > defined outside of the < code > bitflags< / code > macro.< / p >
< p > The struct itself must be a newtype using the bits type as its field.< / p >
< p > The syntax for < code > impl< / code > mode is identical to < code > struct< / code > mode besides the starting token.< / p >
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< h3 id = "examples-1" > < a class = "doc-anchor" href = "#examples-1" > §< / a > Examples< / h3 >
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< p > Implement flags methods and traits for a custom flags type using < code > u8< / code > as its underlying bits type:< / p >
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< div class = "example-wrap" > < pre class = "rust rust-example-rendered" > < code > < span class = "kw" > struct < / span > Flags(u8);
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< span class = "macro" > bitflags!< / span > {
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< span class = "kw" > impl < / span > Flags: u8 {
< span class = "kw" > const < / span > A = < span class = "number" > 1< / span > ;
< span class = "kw" > const < / span > B = < span class = "number" > 1 < / span > < < < span class = "number" > 1< / span > ;
< span class = "kw" > const < / span > C = < span class = "number" > 0b0000_0100< / span > ;
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}
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}< / code > < / pre > < / div >
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< h2 id = "named-and-unnamed-flags" > < a class = "doc-anchor" href = "#named-and-unnamed-flags" > §< / a > Named and unnamed flags< / h2 >
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< p > Constants in the body of a declaration are flags. The identifier of the constant is the name of
the flag. If the identifier is < code > _< / code > , then the flag is unnamed. Unnamed flags don’
generated API, but affect how bits are truncated.< / p >
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< h3 id = "examples-2" > < a class = "doc-anchor" href = "#examples-2" > §< / a > Examples< / h3 >
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< p > Adding an unnamed flag that makes all bits known:< / p >
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< div class = "example-wrap" > < pre class = "rust rust-example-rendered" > < code > < span class = "macro" > bitflags!< / span > {
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< span class = "kw" > struct < / span > Flags: u8 {
< span class = "kw" > const < / span > A = < span class = "number" > 1< / span > ;
< span class = "kw" > const < / span > B = < span class = "number" > 1 < / span > < < < span class = "number" > 1< / span > ;
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< span class = "kw" > const _ < / span > = !< span class = "number" > 0< / span > ;
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}
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}< / code > < / pre > < / div >
< p > Flags types may define multiple unnamed flags:< / p >
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< div class = "example-wrap" > < pre class = "rust rust-example-rendered" > < code > < span class = "macro" > bitflags!< / span > {
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< span class = "kw" > struct < / span > Flags: u8 {
< span class = "kw" > const _ < / span > = < span class = "number" > 1< / span > ;
< span class = "kw" > const _ < / span > = < span class = "number" > 1 < / span > < < < span class = "number" > 1< / span > ;
}
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}< / code > < / pre > < / div >
< / div > < / details > < / section > < / div > < / main > < / body > < / html >
