# Struct proc_macro::TokenStream

1.15.0 · source ·

    pub struct TokenStream(/* private fields */);

Expand description

The main type provided by this crate, representing an abstract stream of tokens, or, more specifically, a sequence of token trees. The type provide interfaces for iterating over those token trees and, conversely, collecting a number of token trees into one stream.

This is both the input and output of `#[proc_macro]`, `#[proc_macro_attribute]` and `#[proc_macro_derive]` definitions.

## Implementations§

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### impl TokenStream

1.29.0 · source

#### pub fn new() -> TokenStream

Returns an empty `TokenStream` containing no token trees.

1.29.0 · source

#### pub fn is_empty(&self) -> bool

Checks if this `TokenStream` is empty.

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#### pub fn expand_expr(&self) -> Result<TokenStream, ExpandError>

🔬This is a nightly-only experimental API. (`proc_macro_expand` #90765)

Parses this `TokenStream` as an expression and attempts to expand any macros within it. Returns the expanded `TokenStream`.

Currently only expressions expanding to literals will succeed, although this may be relaxed in the future.

NOTE: In error conditions, `expand_expr` may leave macros unexpanded, report an error, failing compilation, and/or return an `Err(..)`. The specific behavior for any error condition, and what conditions are considered errors, is unspecified and may change in the future.

## Trait Implementations§

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### impl Clone for TokenStream

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#### fn clone(&self) -> TokenStream

Returns a copy of the value. Read more
1.0.0 · source§

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl Debug for TokenStream

Prints token in a form convenient for debugging.

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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 Default for TokenStream

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#### fn default() -> Self

Returns the “default value” for a type. Read more
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### impl Display for TokenStream

Prints the token stream as a string that is supposed to be losslessly convertible back into the same token stream (modulo spans), except for possibly `TokenTree::Group`s with `Delimiter::None` delimiters and negative numeric literals.

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

Formats the value using the given formatter. Read more
1.30.0 · source§

### impl Extend<TokenStream> for TokenStream

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#### fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I)

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
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#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.30.0 · source§

### impl Extend<TokenTree> for TokenStream

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#### fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, trees: I)

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Extends a collection with exactly one element.
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#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one` #72631)
Reserves capacity in a collection for the given number of additional elements. Read more
1.29.0 · source§

### impl From<TokenTree> for TokenStream

Creates a token stream containing a single token tree.

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#### fn from(tree: TokenTree) -> TokenStream

Converts to this type from the input type.
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### impl FromIterator<TokenStream> for TokenStream

A “flattening” operation on token streams, collects token trees from multiple token streams into a single stream.

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#### fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self

Creates a value from an iterator. Read more
1.29.0 · source§

### impl FromIterator<TokenTree> for TokenStream

Collects a number of token trees into a single stream.

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#### fn from_iter<I: IntoIterator<Item = TokenTree>>(trees: I) -> Self

Creates a value from an iterator. Read more
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### impl FromStr for TokenStream

Attempts to break the string into tokens and parse those tokens into a token stream. May fail for a number of reasons, for example, if the string contains unbalanced delimiters or characters not existing in the language. All tokens in the parsed stream get `Span::call_site()` spans.

NOTE: some errors may cause panics instead of returning `LexError`. We reserve the right to change these errors into `LexError`s later.

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#### type Err = LexError

The associated error which can be returned from parsing.
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#### fn from_str(src: &str) -> Result<TokenStream, LexError>

Parses a string `s` to return a value of this type. Read more
1.29.0 · source§

### impl IntoIterator for TokenStream

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#### type Item = TokenTree

The type of the elements being iterated over.
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#### type IntoIter = IntoIter

Which kind of iterator are we turning this into?
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#### fn into_iter(self) -> IntoIter ⓘ

Creates an iterator from a value. Read more
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### impl !Send for TokenStream

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### impl !Sync for TokenStream

## Auto Trait Implementations§

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### impl RefUnwindSafe for TokenStream

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### impl Unpin for TokenStream

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### impl UnwindSafe for TokenStream

## Blanket Implementations§

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### impl<T> Any for Twhere 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 Twhere 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 Twhere 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> 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 Twhere 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 Twhere 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 Twhere 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 Twhere 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 Twhere 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.