[][src]Struct proc_macro2::Ident

pub struct Ident { /* fields omitted */ }

A word of Rust code, which may be a keyword or legal variable name.

An identifier consists of at least one Unicode code point, the first of which has the XID_Start property and the rest of which have the XID_Continue property.

  • The empty string is not an identifier. Use Option<Ident>.
  • A lifetime is not an identifier. Use syn::Lifetime instead.

An identifier constructed with Ident::new is permitted to be a Rust keyword, though parsing one through its Parse implementation rejects Rust keywords. Use input.call(Ident::parse_any) when parsing to match the behaviour of Ident::new.


A new ident can be created from a string using the Ident::new function. A span must be provided explicitly which governs the name resolution behavior of the resulting identifier.

use proc_macro2::{Ident, Span};

fn main() {
    let call_ident = Ident::new("calligraphy", Span::call_site());

    println!("{}", call_ident);

An ident can be interpolated into a token stream using the quote! macro.

use proc_macro2::{Ident, Span};
use quote::quote;

fn main() {
    let ident = Ident::new("demo", Span::call_site());

    // Create a variable binding whose name is this ident.
    let expanded = quote! { let #ident = 10; };

    // Create a variable binding with a slightly different name.
    let temp_ident = Ident::new(&format!("new_{}", ident), Span::call_site());
    let expanded = quote! { let #temp_ident = 10; };

A string representation of the ident is available through the to_string() method.

// Examine the ident as a string.
let ident_string = ident.to_string();
if ident_string.len() > 60 {
    println!("Very long identifier: {}", ident_string)


impl Ident[src]

pub fn new(string: &str, span: Span) -> Ident[src]

Creates a new Ident with the given string as well as the specified span.

The string argument must be a valid identifier permitted by the language, otherwise the function will panic.

Note that span, currently in rustc, configures the hygiene information for this identifier.

As of this time Span::call_site() explicitly opts-in to "call-site" hygiene meaning that identifiers created with this span will be resolved as if they were written directly at the location of the macro call, and other code at the macro call site will be able to refer to them as well.

Later spans like Span::def_site() will allow to opt-in to "definition-site" hygiene meaning that identifiers created with this span will be resolved at the location of the macro definition and other code at the macro call site will not be able to refer to them.

Due to the current importance of hygiene this constructor, unlike other tokens, requires a Span to be specified at construction.


Panics if the input string is neither a keyword nor a legal variable name. If you are not sure whether the string contains an identifier and need to handle an error case, use syn::parse_str::<Ident> rather than Ident::new.

pub fn new_raw(string: &str, span: Span) -> Ident[src]

Same as Ident::new, but creates a raw identifier (r#ident).

This method is semver exempt and not exposed by default.

pub fn span(&self) -> Span[src]

Returns the span of this Ident.

pub fn set_span(&mut self, span: Span)[src]

Configures the span of this Ident, possibly changing its hygiene context.

Trait Implementations

impl Clone for Ident[src]

impl Debug for Ident[src]

impl Display for Ident[src]

Prints the identifier as a string that should be losslessly convertible back into the same identifier.

impl Eq for Ident[src]

impl From<Ident> for TokenTree[src]

impl Hash for Ident[src]

impl Ord for Ident[src]

impl PartialEq<Ident> for Ident[src]

impl<T: ?Sized> PartialEq<T> for Ident where
    T: AsRef<str>, 

impl PartialOrd<Ident> for Ident[src]

Auto Trait Implementations

impl !RefUnwindSafe for Ident

impl !Send for Ident

impl !Sync for Ident

impl Unpin for Ident

impl UnwindSafe for Ident

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized

impl<T> Borrow<T> for T where
    T: ?Sized

impl<T> BorrowMut<T> for T where
    T: ?Sized

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 

impl<T> ToOwned for T where
    T: Clone

type Owned = T

The resulting type after obtaining ownership.

impl<T> ToString for T where
    T: Display + ?Sized

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.