proc_macro2

Struct Ident

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pub struct Ident { /* private fields */ }
Expand description

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.

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

Implementations§

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impl Ident

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pub 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.

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pub 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.

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pub fn span(&self) -> Span

Returns the span of this Ident.

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

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

Trait Implementations§

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impl Clone for Ident

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fn clone(&self) -> Ident

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for Ident

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

Formats the value using the given formatter. Read more
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impl Display for Ident

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

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

Formats the value using the given formatter. Read more
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impl From<Ident> for TokenTree

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fn from(g: Ident) -> Self

Converts to this type from the input type.
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impl Hash for Ident

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

Feeds this value into the given Hasher. Read more
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fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl Ord for Ident

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

This method returns an Ordering between self and other. Read more
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fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
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fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
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fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized,

Restrict a value to a certain interval. Read more
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impl<T> PartialEq<T> for Ident
where T: ?Sized + AsRef<str>,

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

Tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

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

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

Tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

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

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

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator. Read more
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impl Eq for Ident

Auto Trait Implementations§

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impl Freeze for Ident

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impl RefUnwindSafe for Ident

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impl !Send for Ident

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impl !Sync for Ident

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impl Unpin for Ident

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impl UnwindSafe for Ident

Blanket Implementations§

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

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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

Mutably borrows from an owned value. Read more
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impl<T> CloneToUninit for T
where T: Clone,

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unsafe fn clone_to_uninit(&self, dst: *mut T)

🔬This is a nightly-only experimental API. (clone_to_uninit)
Performs copy-assignment from self to dst. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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

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fn into(self) -> U

Calls U::from(self).

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

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

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T> ToString for T
where T: Display + ?Sized,

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default fn to_string(&self) -> String

Converts the given value to a String. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.