[][src]Struct syn::Attribute

pub struct Attribute {
    pub pound_token: Pound,
    pub style: AttrStyle,
    pub bracket_token: Bracket,
    pub path: Path,
    pub tts: TokenStream,
}

An attribute like #[repr(transparent)].

This type is available if Syn is built with the "derive" or "full" feature.

Syntax

Rust has six types of attributes.

  • Outer attributes like #[repr(transparent)]. These appear outside or in front of the item they describe.
  • Inner attributes like #![feature(proc_macro)]. These appear inside of the item they describe, usually a module.
  • Outer doc comments like /// # Example.
  • Inner doc comments like //! Please file an issue.
  • Outer block comments /** # Example */.
  • Inner block comments /*! Please file an issue */.

The style field of type AttrStyle distinguishes whether an attribute is outer or inner. Doc comments and block comments are promoted to attributes, as this is how they are processed by the compiler and by macro_rules! macros.

The path field gives the possibly colon-delimited path against which the attribute is resolved. It is equal to "doc" for desugared doc comments. The tts field contains the rest of the attribute body as tokens.

#[derive(Copy)]      #[crate::precondition x < 5]
  ^^^^^^~~~~~~         ^^^^^^^^^^^^^^^^^^^ ~~~~~
   path  tts                   path         tts

Use the parse_meta method to try parsing the tokens of an attribute into the structured representation that is used by convention across most Rust libraries.

Parsing

This type does not implement the Parse trait and thus cannot be parsed directly by ParseStream::parse. Instead use ParseStream::call with one of the two parser functions Attribute::parse_outer or Attribute::parse_inner depending on which you intend to parse.

#[macro_use]
extern crate syn;

use syn::{Attribute, Ident, Result};
use syn::parse::{Parse, ParseStream};

// Parses a unit struct with attributes.
//
//     #[path = "s.tmpl"]
//     struct S;
struct UnitStruct {
    attrs: Vec<Attribute>,
    struct_token: Token![struct],
    name: Ident,
    semi_token: Token![;],
}

impl Parse for UnitStruct {
    fn parse(input: ParseStream) -> Result<Self> {
        Ok(UnitStruct {
            attrs: input.call(Attribute::parse_outer)?,
            struct_token: input.parse()?,
            name: input.parse()?,
            semi_token: input.parse()?,
        })
    }
}

Fields

Methods

impl Attribute
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Parses the tokens after the path as a Meta if possible.

Parses zero or more outer attributes from the stream.

This function is available if Syn is built with the "parsing" feature.

Parses zero or more inner attributes from the stream.

This function is available if Syn is built with the "parsing" feature.

Trait Implementations

impl Clone for Attribute
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Performs copy-assignment from source. Read more

impl Eq for Attribute
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impl PartialEq<Attribute> for Attribute
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This method tests for !=.

impl Debug for Attribute
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impl Hash for Attribute
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Feeds a slice of this type into the given [Hasher]. Read more

impl ToTokens for Attribute
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Convert self directly into a TokenStream object. Read more

Auto Trait Implementations

impl !Send for Attribute

impl !Sync for Attribute

Blanket Implementations

impl<T> Spanned for T where
    T: ToTokens
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impl<T> From for T
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impl<T, U> Into for T where
    U: From<T>, 
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impl<T> ToOwned for T where
    T: Clone
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impl<T, U> TryFrom for T where
    T: From<U>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

impl<T> Borrow for T where
    T: ?Sized
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impl<T> Any for T where
    T: 'static + ?Sized
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impl<T, U> TryInto for T where
    U: TryFrom<T>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

impl<T> BorrowMut for T where
    T: ?Sized
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impl<E> SpecializationError for E
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impl<T> Erased for T
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impl<T> Send for T where
    T: ?Sized
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impl<T> Sync for T where
    T: ?Sized
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impl<T> Erased for T