Enum syn::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

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

This method 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 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> 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.