# Pat in syn - Rust
A pattern in a local binding, function signature, match expression, or various other places.

syn

# Enum Pat

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    #[non_exhaustive]pub enum Pat {
    Show 17 variants    Const(PatConst),
        Ident(PatIdent),
        Lit(PatLit),
        Macro(PatMacro),
        Or(PatOr),
        Paren(PatParen),
        Path(PatPath),
        Range(PatRange),
        Reference(PatReference),
        Rest(PatRest),
        Slice(PatSlice),
        Struct(PatStruct),
        Tuple(PatTuple),
        TupleStruct(PatTupleStruct),
        Type(PatType),
        Verbatim(TokenStream),
        Wild(PatWild),
    }

Expand description

A pattern in a local binding, function signature, match expression, or various other places.

## §Syntax tree enum

This type is a syntax tree enum.

## Variants (Non-exhaustive)§

This enum is marked as non-exhaustive
Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.
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### Const(PatConst)

A const block: `const { ... }`.

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### Ident(PatIdent)

A pattern that binds a new variable: `ref mut binding @ SUBPATTERN`.

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### Lit(PatLit)

A literal pattern: `0`.

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### Macro(PatMacro)

A macro in pattern position.

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### Or(PatOr)

A pattern that matches any one of a set of cases.

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### Paren(PatParen)

A parenthesized pattern: `(A | B)`.

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### Path(PatPath)

A path pattern like `Color::Red`, optionally qualified with a self-type.

Unqualified path patterns can legally refer to variants, structs, constants or associated constants. Qualified path patterns like `<A>::B::C` and `<A as Trait>::B::C` can only legally refer to associated constants.

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### Range(PatRange)

A range pattern: `1..=2`.

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### Reference(PatReference)

A reference pattern: `&mut var`.

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### Rest(PatRest)

The dots in a tuple or slice pattern: `[0, 1, ..]`.

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### Slice(PatSlice)

A dynamically sized slice pattern: `[a, b, ref i @ .., y, z]`.

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### Struct(PatStruct)

A struct or struct variant pattern: `Variant { x, y, .. }`.

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### Tuple(PatTuple)

A tuple pattern: `(a, b)`.

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### TupleStruct(PatTupleStruct)

A tuple struct or tuple variant pattern: `Variant(x, y, .., z)`.

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### Type(PatType)

A type ascription pattern: `foo: f64`.

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### Verbatim(TokenStream)

Tokens in pattern position not interpreted by Syn.

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### Wild(PatWild)

A pattern that matches any value: `_`.

## Implementations§

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### impl Pat

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#### pub fn parse_single(input: ParseStream<'_>) -> Result<Self>

Parse a pattern that does not involve `|` at the top level.

This parser matches the behavior of the `$:pat_param` macro_rules matcher, and on editions prior to Rust 2021, the behavior of `$:pat`.

In Rust syntax, some examples of where this syntax would occur are in the argument pattern of functions and closures. Patterns using `|` are not allowed to occur in these positions.

ⓘ

    fn f(Some(_) | None: Option<T>) {
        let _ = |Some(_) | None: Option<T>| {};
        //       ^^^^^^^^^^^^^^^^^^^^^^^^^??? :(
    }

    error: top-level or-patterns are not allowed in function parameters
     --> src/main.rs:1:6
      |
    1 | fn f(Some(_) | None: Option<T>) {
      |      ^^^^^^^^^^^^^^ help: wrap the pattern in parentheses: `(Some(_) | None)`

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#### pub fn parse_multi(input: ParseStream<'_>) -> Result<Self>

Parse a pattern, possibly involving `|`, but not a leading `|`.

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#### pub fn parse_multi_with_leading_vert(input: ParseStream<'_>) -> Result<Self>

Parse a pattern, possibly involving `|`, possibly including a leading `|`.

This parser matches the behavior of the Rust 2021 edition’s `$:pat` macro_rules matcher.

In Rust syntax, an example of where this syntax would occur is in the pattern of a `match` arm, where the language permits an optional leading `|`, although it is not idiomatic to write one there in handwritten code.

    match wat {
        | None | Some(false) => {}
        | Some(true) => {}
    }

The compiler accepts it only to facilitate some situations in macro-generated code where a macro author might need to write:

    match $value {
        $(| $conditions1)* $(| $conditions2)* => $then
    }

Expressing the same thing correctly in the case that either one (but not both) of `$conditions1` and `$conditions2` might be empty, without leading `|`, is complex.

Use `Pat::parse_multi` instead if you are not intending to support macro-generated macro input.

## Trait Implementations§

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### impl Clone for Pat

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

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 Pat

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

Formats the value using the given formatter. Read more
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### impl From<ExprConst> for Pat

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#### fn from(e: PatConst) -> Pat

Converts to this type from the input type.
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### impl From<ExprLit> for Pat

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#### fn from(e: PatLit) -> Pat

Converts to this type from the input type.
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### impl From<ExprMacro> for Pat

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#### fn from(e: PatMacro) -> Pat

Converts to this type from the input type.
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### impl From<ExprPath> for Pat

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#### fn from(e: PatPath) -> Pat

Converts to this type from the input type.
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### impl From<ExprRange> for Pat

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#### fn from(e: PatRange) -> Pat

Converts to this type from the input type.
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### impl From<PatIdent> for Pat

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#### fn from(e: PatIdent) -> Pat

Converts to this type from the input type.
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### impl From<PatOr> for Pat

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#### fn from(e: PatOr) -> Pat

Converts to this type from the input type.
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### impl From<PatParen> for Pat

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#### fn from(e: PatParen) -> Pat

Converts to this type from the input type.
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### impl From<PatReference> for Pat

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#### fn from(e: PatReference) -> Pat

Converts to this type from the input type.
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### impl From<PatRest> for Pat

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#### fn from(e: PatRest) -> Pat

Converts to this type from the input type.
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### impl From<PatSlice> for Pat

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#### fn from(e: PatSlice) -> Pat

Converts to this type from the input type.
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### impl From<PatStruct> for Pat

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#### fn from(e: PatStruct) -> Pat

Converts to this type from the input type.
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### impl From<PatTuple> for Pat

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#### fn from(e: PatTuple) -> Pat

Converts to this type from the input type.
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### impl From<PatTupleStruct> for Pat

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#### fn from(e: PatTupleStruct) -> Pat

Converts to this type from the input type.
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### impl From<PatType> for Pat

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#### fn from(e: PatType) -> Pat

Converts to this type from the input type.
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### impl From<PatWild> for Pat

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#### fn from(e: PatWild) -> Pat

Converts to this type from the input type.
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### impl Hash for Pat

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#### fn hash<H>(&self, state: &mut H)
where H: Hasher,

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 PartialEq for Pat

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#### fn eq(&self, other: &Self) -> 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 ToTokens for Pat

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#### fn to_tokens(&self, tokens: &mut TokenStream)

Write `self` to the given `TokenStream`. Read more
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#### fn to_token_stream(&self) -> TokenStream

Convert `self` directly into a `TokenStream` object. Read more
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#### fn into_token_stream(self) -> TokenStream
where Self: Sized,

Convert `self` directly into a `TokenStream` object. Read more
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### impl Eq for Pat

## Auto Trait Implementations§

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### impl Freeze for Pat

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### impl RefUnwindSafe for Pat

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### impl !Send for Pat

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### impl !Sync for Pat

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### impl Unpin for Pat

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### impl UnwindSafe for Pat

## 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 u8)

🔬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> Spanned for T
where T: Spanned + ?Sized,

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#### fn span(&self) -> Span

Returns a `Span` covering the complete contents of this syntax tree node, or `Span::call_site()` if this node is empty.
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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, 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.