Enum `Pat`

enum Pat

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

Const(PatConst)

A const block: const { ... }.

Ident(PatIdent)

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

Lit(PatLit)

A literal pattern: 0.

Macro(PatMacro)

A macro in pattern position.

Or(PatOr)

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

Paren(PatParen)

A parenthesized pattern: (A | B).

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.

Range(PatRange)

A range pattern: 1..=2.

Reference(PatReference)

A reference pattern: &mut var.

Rest(PatRest)

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

Slice(PatSlice)

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

Struct(PatStruct)

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

Tuple(PatTuple)

A tuple pattern: (a, b).

TupleStruct(PatTupleStruct)

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

Type(PatType)

A type ascription pattern: foo: f64.

Verbatim(proc_macro2::TokenStream)

Tokens in pattern position not interpreted by Syn.

Wild(PatWild)

A pattern that matches any value: _.

Implementations

`impl Pat`

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)`

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

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

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.

# let wat = None;
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:

# macro_rules! doc {
#     ($value:expr, ($($conditions1:pat),*), ($($conditions2:pat),*), $then:expr) => {
match $value {
    $(| $conditions1)* $(| $conditions2)* => $then
}
#     };
# }
#
# doc!(true, (true), (false), {});
# doc!(true, (), (true, false), {});
# doc!(true, (true, false), (), {});

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.

`impl Clone for Pat`

fn clone(self: &Self) -> Self

`impl Debug for Pat`

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

`impl Eq for Pat`

`impl Freeze for Pat`

`impl From for Pat`

fn from(e: PatRest) -> Pat

`impl From for Pat`

fn from(e: PatType) -> Pat

`impl From for Pat`

fn from(e: PatOr) -> Pat

`impl From for Pat`

fn from(e: PatStruct) -> Pat

`impl From for Pat`

fn from(e: PatConst) -> Pat

`impl From for Pat`

fn from(e: PatMacro) -> Pat

`impl From for Pat`

fn from(e: PatReference) -> Pat

`impl From for Pat`

fn from(e: PatTupleStruct) -> Pat

`impl From for Pat`

fn from(e: PatLit) -> Pat

`impl From for Pat`

fn from(e: PatIdent) -> Pat

`impl From for Pat`

fn from(e: PatPath) -> Pat

`impl From for Pat`

fn from(e: PatSlice) -> Pat

`impl From for Pat`

fn from(e: PatWild) -> Pat

`impl From for Pat`

fn from(e: PatRange) -> Pat

`impl From for Pat`

fn from(e: PatParen) -> Pat

`impl From for Pat`

fn from(e: PatTuple) -> Pat

`impl Hash for Pat`

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

`impl PartialEq for Pat`

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

`impl RefUnwindSafe for Pat`

`impl Send for Pat`

`impl Sync for Pat`

`impl ToTokens for Pat`

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

`impl Unpin for Pat`

`impl UnsafeUnpin for Pat`

`impl UnwindSafe for Pat`

`impl<T> Any for Pat`

fn type_id(self: &Self) -> TypeId

`impl<T> Borrow for Pat`

fn borrow(self: &Self) -> &T

`impl<T> BorrowMut for Pat`

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

`impl<T> CloneToUninit for Pat`

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

`impl<T> From for Pat`

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

`impl<T> Spanned for Pat`

fn span(self: &Self) -> Span

`impl<T> ToOwned for Pat`

fn to_owned(self: &Self) -> T
fn clone_into(self: &Self, target: &mut T)

`impl<T, U> Into for Pat`

fn into(self: 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 Pat`

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

`impl<T, U> TryInto for Pat`

fn try_into(self: Self) -> Result<U, <U as TryFrom<T>>::Error>