Enum Pat

#[non_exhaustive]
pub enum Pat {
    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),
}

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)

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.

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(TokenStream)

Tokens in pattern position not interpreted by Syn.

Wild(PatWild)

A pattern that matches any value: _.

Implementations

impl Pat

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)`

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

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

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

impl Clone for Pat

fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

impl From<ExprConst> for Pat

fn from(e: PatConst) -> Pat

Converts to this type from the input type.

impl From<ExprLit> for Pat

fn from(e: PatLit) -> Pat

Converts to this type from the input type.

impl From<ExprMacro> for Pat

fn from(e: PatMacro) -> Pat

Converts to this type from the input type.

impl From<ExprPath> for Pat

fn from(e: PatPath) -> Pat

Converts to this type from the input type.

impl From<ExprRange> for Pat

fn from(e: PatRange) -> Pat

Converts to this type from the input type.

impl From<PatIdent> for Pat

fn from(e: PatIdent) -> Pat

Converts to this type from the input type.

impl From<PatOr> for Pat

fn from(e: PatOr) -> Pat

Converts to this type from the input type.

impl From<PatParen> for Pat

fn from(e: PatParen) -> Pat

Converts to this type from the input type.

impl From<PatReference> for Pat

fn from(e: PatReference) -> Pat

Converts to this type from the input type.

impl From<PatRest> for Pat

fn from(e: PatRest) -> Pat

Converts to this type from the input type.

impl From<PatSlice> for Pat

fn from(e: PatSlice) -> Pat

Converts to this type from the input type.

impl From<PatStruct> for Pat

fn from(e: PatStruct) -> Pat

Converts to this type from the input type.

impl From<PatTuple> for Pat

fn from(e: PatTuple) -> Pat

Converts to this type from the input type.

impl From<PatTupleStruct> for Pat

fn from(e: PatTupleStruct) -> Pat

Converts to this type from the input type.

impl From<PatType> for Pat

fn from(e: PatType) -> Pat

Converts to this type from the input type.

impl From<PatWild> for Pat

fn from(e: PatWild) -> Pat

Converts to this type from the input type.

impl ToTokens for Pat

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

Write self to the given TokenStream.

fn to_token_stream(&self) -> TokenStream

Convert self directly into a TokenStream object.

fn into_token_stream(self) -> TokenStream

where Self: Sized,

Convert self directly into a TokenStream object.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 184 bytes

Size for each variant:

• Const: 80 bytes
• Ident: 88 bytes
• Lit: 56 bytes
• Macro: 136 bytes
• Or: 72 bytes
• Paren: 56 bytes
• Path: 112 bytes
• Range: 64 bytes
• Reference: 56 bytes
• Rest: 40 bytes
• Slice: 80 bytes
• Struct: 184 bytes
• Tuple: 80 bytes
• TupleStruct: 160 bytes
• Type: 56 bytes
• Verbatim: 40 bytes
• Wild: 40 bytes