Struct `Ident`

pub struct Ident { /* private fields */ }

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.

Examples

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.

# use proc_macro2::{Ident, Span};
#
# let ident = Ident::new("another_identifier", Span::call_site());
#
// Examine the ident as a string.
let ident_string = ident.to_string();
if ident_string.len() > 60 {
    println!("Very long identifier: {}", ident_string)
}

Implementations

`impl Ident`

fn new(string: &str, span: Span) -> Self

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

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.

fn new_raw(string: &str, span: Span) -> Self

Same as Ident::new, but creates a raw identifier (r#ident). The string argument must be a valid identifier permitted by the language (including keywords, e.g. fn). Keywords which are usable in path segments (e.g. self, super) are not supported, and will cause a panic.

fn span(&self) -> Span

Returns the span of this Ident.

fn set_span(&mut self, span: Span)

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

Trait Implementations

`impl Clone for Ident`

fn clone(&self) -> Self

`impl Debug for Ident`

fn fmt(&self, f: &mut Formatter<'_>) -> Result

`impl Display for Ident`

fn fmt(&self, f: &mut Formatter<'_>) -> Result

`impl Eq for Ident`

`impl Hash for Ident`

fn hash<H: Hasher>(&self, hasher: &mut H)

`impl Ord for Ident`

fn cmp(&self, other: &Ident) -> Ordering

`impl PartialEq for Ident`

fn eq(&self, other: &Ident) -> bool

`impl PartialOrd for Ident`

fn partial_cmp(&self, other: &Ident) -> Option<Ordering>

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

fn eq(&self, other: &T) -> bool

Auto Trait Implementations

`impl !Send for Ident`

`impl !Sync for Ident`

`impl Freeze for Ident`

`impl RefUnwindSafe for Ident`

`impl Unpin for Ident`

`impl UnsafeUnpin for Ident`

`impl UnwindSafe for Ident`

Blanket Implementations

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

fn type_id(&self) -> TypeId

`impl<T> Borrow<T> for Ident where T: ?Sized,`

fn borrow(&self) -> &T

`impl<T> BorrowMut<T> for Ident where T: ?Sized,`

fn borrow_mut(&mut self) -> &mut T

`impl<T> CloneToUninit for Ident where T: Clone,`

unsafe fn clone_to_uninit(&self, dest: *mut u8)

`impl<T> From<T> for Ident`

fn from(t: T) -> T: Returns the argument unchanged.

`impl<T> ToOwned for Ident where T: Clone,`

type Owned = T;
fn to_owned(&self) -> T
fn clone_into(&self, target: &mut T)

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

fn to_string(&self) -> String

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

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of [From]<T> for U chooses to do.

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

type Error = never;
fn try_from(value: U) -> Result<T, never>

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

type Error = >::Error;
fn try_into(self) -> Result<U, >::Error>