Enum syn::Expr

pub enum Expr {
    Box(ExprBox),
    InPlace(ExprInPlace),
    Array(ExprArray),
    Call(ExprCall),
    MethodCall(ExprMethodCall),
    Tuple(ExprTuple),
    Binary(ExprBinary),
    Unary(ExprUnary),
    Lit(ExprLit),
    Cast(ExprCast),
    Type(ExprType),
    Let(ExprLet),
    If(ExprIf),
    While(ExprWhile),
    ForLoop(ExprForLoop),
    Loop(ExprLoop),
    Match(ExprMatch),
    Closure(ExprClosure),
    Unsafe(ExprUnsafe),
    Block(ExprBlock),
    Assign(ExprAssign),
    AssignOp(ExprAssignOp),
    Field(ExprField),
    Index(ExprIndex),
    Range(ExprRange),
    Path(ExprPath),
    Reference(ExprReference),
    Break(ExprBreak),
    Continue(ExprContinue),
    Return(ExprReturn),
    Macro(ExprMacro),
    Struct(ExprStruct),
    Repeat(ExprRepeat),
    Paren(ExprParen),
    Group(ExprGroup),
    Try(ExprTry),
    Async(ExprAsync),
    TryBlock(ExprTryBlock),
    Yield(ExprYield),
    Verbatim(ExprVerbatim),
}

A Rust expression.

This type is available if Syn is built with the "derive" or "full" feature.

Syntax tree enums

This type is a syntax tree enum. In Syn this and other syntax tree enums are designed to be traversed using the following rebinding idiom.

# use syn::Expr;
#
# fn example(expr: Expr) {
# const IGNORE: &str = stringify! {
let expr: Expr = /* ... */;
# };
match expr {
    Expr::MethodCall(expr) => {
        /* ... */
    }
    Expr::Cast(expr) => {
        /* ... */
    }
    Expr::If(expr) => {
        /* ... */
    }

    /* ... */
    # _ => {}
# }
# }

We begin with a variable expr of type Expr that has no fields (because it is an enum), and by matching on it and rebinding a variable with the same name expr we effectively imbue our variable with all of the data fields provided by the variant that it turned out to be. So for example above if we ended up in the MethodCall case then we get to use expr.receiver, expr.args etc; if we ended up in the If case we get to use expr.cond, expr.then_branch, expr.else_branch.

This approach avoids repeating the variant names twice on every line.

# use syn::{Expr, ExprMethodCall};
#
# fn example(expr: Expr) {
// Repetitive; recommend not doing this.
match expr {
    Expr::MethodCall(ExprMethodCall { method, args, .. }) => {
# }
# _ => {}
# }
# }

In general, the name to which a syntax tree enum variant is bound should be a suitable name for the complete syntax tree enum type.

# use syn::{Expr, ExprField};
#
# fn example(discriminant: ExprField) {
// Binding is called `base` which is the name I would use if I were
// assigning `*discriminant.base` without an `if let`.
if let Expr::Tuple(base) = *discriminant.base {
# }
# }

A sign that you may not be choosing the right variable names is if you see names getting repeated in your code, like accessing receiver.receiver or pat.pat or cond.cond.

Variants

Box(ExprBox)

A box expression: box f.

This type is available if Syn is built with the "full" feature.

InPlace(ExprInPlace)

A placement expression: place <- value.

This type is available if Syn is built with the "full" feature.

Array(ExprArray)

A slice literal expression: [a, b, c, d].

This type is available if Syn is built with the "full" feature.

Call(ExprCall)

A function call expression: invoke(a, b).

This type is available if Syn is built with the "derive" or "full" feature.

MethodCall(ExprMethodCall)

A method call expression: x.foo::<T>(a, b).

This type is available if Syn is built with the "full" feature.

Tuple(ExprTuple)

A tuple expression: (a, b, c, d).

This type is available if Syn is built with the "full" feature.

Binary(ExprBinary)

A binary operation: a + b, a * b.

This type is available if Syn is built with the "derive" or "full" feature.

Unary(ExprUnary)

A unary operation: !x, *x.

This type is available if Syn is built with the "derive" or "full" feature.

Lit(ExprLit)

A literal in place of an expression: 1, "foo".

This type is available if Syn is built with the "derive" or "full" feature.

Cast(ExprCast)

A cast expression: foo as f64.

This type is available if Syn is built with the "derive" or "full" feature.

Type(ExprType)

A type ascription expression: foo: f64.

This type is available if Syn is built with the "full" feature.

Let(ExprLet)

A let guard: let Some(x) = opt.

This type is available if Syn is built with the "full" feature.

If(ExprIf)

An if expression with an optional else block: if expr { ... } else { ... }.

The else branch expression may only be an If or Block expression, not any of the other types of expression.

This type is available if Syn is built with the "full" feature.

While(ExprWhile)

A while loop: while expr { ... }.

This type is available if Syn is built with the "full" feature.

ForLoop(ExprForLoop)

A for loop: for pat in expr { ... }.

This type is available if Syn is built with the "full" feature.

Loop(ExprLoop)

Conditionless loop: loop { ... }.

This type is available if Syn is built with the "full" feature.

Match(ExprMatch)

A match expression: match n { Some(n) => {}, None => {} }.

This type is available if Syn is built with the "full" feature.

Closure(ExprClosure)

A closure expression: |a, b| a + b.

This type is available if Syn is built with the "full" feature.

Unsafe(ExprUnsafe)

An unsafe block: unsafe { ... }.

This type is available if Syn is built with the "full" feature.

Block(ExprBlock)

A blocked scope: { ... }.

This type is available if Syn is built with the "full" feature.

Assign(ExprAssign)

An assignment expression: a = compute().

This type is available if Syn is built with the "full" feature.

AssignOp(ExprAssignOp)

A compound assignment expression: counter += 1.

This type is available if Syn is built with the "full" feature.

Field(ExprField)

Access of a named struct field (obj.k) or unnamed tuple struct field (obj.0).

This type is available if Syn is built with the "full" feature.

Index(ExprIndex)

A square bracketed indexing expression: vector[2].

This type is available if Syn is built with the "derive" or "full" feature.

Range(ExprRange)

A range expression: 1..2, 1.., ..2, 1..=2, ..=2.

This type is available if Syn is built with the "full" feature.

Path(ExprPath)

A path like std::mem::replace possibly containing generic parameters and a qualified self-type.

A plain identifier like x is a path of length 1.

This type is available if Syn is built with the "derive" or "full" feature.

Reference(ExprReference)

A referencing operation: &a or &mut a.

This type is available if Syn is built with the "full" feature.

Break(ExprBreak)

A break, with an optional label to break and an optional expression.

This type is available if Syn is built with the "full" feature.

Continue(ExprContinue)

A continue, with an optional label.

This type is available if Syn is built with the "full" feature.

Return(ExprReturn)

A return, with an optional value to be returned.

This type is available if Syn is built with the "full" feature.

Macro(ExprMacro)

A macro invocation expression: format!("{}", q).

This type is available if Syn is built with the "full" feature.

Struct(ExprStruct)

A struct literal expression: Point { x: 1, y: 1 }.

The rest provides the value of the remaining fields as in S { a: 1, b: 1, ..rest }.

This type is available if Syn is built with the "full" feature.

Repeat(ExprRepeat)

An array literal constructed from one repeated element: [0u8; N].

This type is available if Syn is built with the "full" feature.

Paren(ExprParen)

A parenthesized expression: (a + b).

This type is available if Syn is built with the "full" feature.

Group(ExprGroup)

An expression contained within invisible delimiters.

This variant is important for faithfully representing the precedence of expressions and is related to None-delimited spans in a TokenStream.

This type is available if Syn is built with the "full" feature.

Try(ExprTry)

A try-expression: expr?.

This type is available if Syn is built with the "full" feature.

Async(ExprAsync)

An async block: async { ... }.

This type is available if Syn is built with the "full" feature.

TryBlock(ExprTryBlock)

A try block: try { ... }.

This type is available if Syn is built with the "full" feature.

Yield(ExprYield)

A yield expression: yield expr.

This type is available if Syn is built with the "full" feature.

Verbatim(ExprVerbatim)

Tokens in expression position not interpreted by Syn.

This type is available if Syn is built with the "derive" or "full" feature.

Trait Implementations

impl Parse for Expr

fn parse(input: ParseStream) -> Result<Self>

impl Clone for Expr

fn clone(&self) -> Expr

Returns a copy of the value.

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

Performs copy-assignment from source.

impl From<ExprBox> for Expr

fn from(e: ExprBox) -> Expr

Performs the conversion.

impl From<ExprInPlace> for Expr

fn from(e: ExprInPlace) -> Expr

Performs the conversion.

impl From<ExprArray> for Expr

fn from(e: ExprArray) -> Expr

Performs the conversion.

impl From<ExprCall> for Expr

fn from(e: ExprCall) -> Expr

Performs the conversion.

impl From<ExprMethodCall> for Expr

fn from(e: ExprMethodCall) -> Expr

Performs the conversion.

impl From<ExprTuple> for Expr

fn from(e: ExprTuple) -> Expr

Performs the conversion.

impl From<ExprBinary> for Expr

fn from(e: ExprBinary) -> Expr

Performs the conversion.

impl From<ExprUnary> for Expr

fn from(e: ExprUnary) -> Expr

Performs the conversion.

impl From<ExprLit> for Expr

fn from(e: ExprLit) -> Expr

Performs the conversion.

impl From<ExprCast> for Expr

fn from(e: ExprCast) -> Expr

Performs the conversion.

impl From<ExprType> for Expr

fn from(e: ExprType) -> Expr

Performs the conversion.

impl From<ExprLet> for Expr

fn from(e: ExprLet) -> Expr

Performs the conversion.

impl From<ExprIf> for Expr

fn from(e: ExprIf) -> Expr

Performs the conversion.

impl From<ExprWhile> for Expr

fn from(e: ExprWhile) -> Expr

Performs the conversion.

impl From<ExprForLoop> for Expr

fn from(e: ExprForLoop) -> Expr

Performs the conversion.

impl From<ExprLoop> for Expr

fn from(e: ExprLoop) -> Expr

Performs the conversion.

impl From<ExprMatch> for Expr

fn from(e: ExprMatch) -> Expr

Performs the conversion.

impl From<ExprClosure> for Expr

fn from(e: ExprClosure) -> Expr

Performs the conversion.

impl From<ExprUnsafe> for Expr

fn from(e: ExprUnsafe) -> Expr

Performs the conversion.

impl From<ExprBlock> for Expr

fn from(e: ExprBlock) -> Expr

Performs the conversion.

impl From<ExprAssign> for Expr

fn from(e: ExprAssign) -> Expr

Performs the conversion.

impl From<ExprAssignOp> for Expr

fn from(e: ExprAssignOp) -> Expr

Performs the conversion.

impl From<ExprField> for Expr

fn from(e: ExprField) -> Expr

Performs the conversion.

impl From<ExprIndex> for Expr

fn from(e: ExprIndex) -> Expr

Performs the conversion.

impl From<ExprRange> for Expr

fn from(e: ExprRange) -> Expr

Performs the conversion.

impl From<ExprPath> for Expr

fn from(e: ExprPath) -> Expr

Performs the conversion.

impl From<ExprReference> for Expr

fn from(e: ExprReference) -> Expr

Performs the conversion.

impl From<ExprBreak> for Expr

fn from(e: ExprBreak) -> Expr

Performs the conversion.

impl From<ExprContinue> for Expr

fn from(e: ExprContinue) -> Expr

Performs the conversion.

impl From<ExprReturn> for Expr

fn from(e: ExprReturn) -> Expr

Performs the conversion.

impl From<ExprMacro> for Expr

fn from(e: ExprMacro) -> Expr

Performs the conversion.

impl From<ExprStruct> for Expr

fn from(e: ExprStruct) -> Expr

Performs the conversion.

impl From<ExprRepeat> for Expr

fn from(e: ExprRepeat) -> Expr

Performs the conversion.

impl From<ExprParen> for Expr

fn from(e: ExprParen) -> Expr

Performs the conversion.

impl From<ExprGroup> for Expr

fn from(e: ExprGroup) -> Expr

Performs the conversion.

impl From<ExprTry> for Expr

fn from(e: ExprTry) -> Expr

Performs the conversion.

impl From<ExprAsync> for Expr

fn from(e: ExprAsync) -> Expr

Performs the conversion.

impl From<ExprTryBlock> for Expr

fn from(e: ExprTryBlock) -> Expr

Performs the conversion.

impl From<ExprYield> for Expr

fn from(e: ExprYield) -> Expr

Performs the conversion.

impl From<ExprVerbatim> for Expr

fn from(e: ExprVerbatim) -> Expr

Performs the conversion.

impl ToTokens for Expr

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

Write self to the given TokenStream.

fn into_token_stream(self) -> TokenStream

Convert self directly into a TokenStream object.