# Struct syn::Macro

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    pub struct Macro {
        pub path: Path,
        pub bang_token: Bang,
        pub delimiter: MacroDelimiter,
        pub tokens: TokenStream,
    }

Expand description

A macro invocation: `println!("{}", mac)`.

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

## Fields

`path: Path` `bang_token: Bang` `delimiter: MacroDelimiter` `tokens: TokenStream`

## Implementations

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### impl Macro

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#### pub fn parse_body<T: Parse>(&self) -> Result<T>

Parse the tokens within the macro invocation’s delimiters into a syntax tree.

This is equivalent to `syn::parse2::<T>(mac.tokens)` except that it produces a more useful span when `tokens` is empty.

##### Example

    use syn::{parse_quote, Expr, ExprLit, Ident, Lit, LitStr, Macro, Token};
    use syn::ext::IdentExt;
    use syn::parse::{Error, Parse, ParseStream, Result};
    use syn::punctuated::Punctuated;

    // The arguments expected by libcore's format_args macro, and as a
    // result most other formatting and printing macros like println.
    //
    //     println!("{} is {number:.prec$}", "x", prec=5, number=0.01)
    struct FormatArgs {
        format_string: Expr,
        positional_args: Vec<Expr>,
        named_args: Vec<(Ident, Expr)>,
    }

    impl Parse for FormatArgs {
        fn parse(input: ParseStream) -> Result<Self> {
            let format_string: Expr;
            let mut positional_args = Vec::new();
            let mut named_args = Vec::new();

            format_string = input.parse()?;
            while !input.is_empty() {
                input.parse::<Token![,]>()?;
                if input.is_empty() {
                    break;
                }
                if input.peek(Ident::peek_any) && input.peek2(Token![=]) {
                    while !input.is_empty() {
                        let name: Ident = input.call(Ident::parse_any)?;
                        input.parse::<Token![=]>()?;
                        let value: Expr = input.parse()?;
                        named_args.push((name, value));
                        if input.is_empty() {
                            break;
                        }
                        input.parse::<Token![,]>()?;
                    }
                    break;
                }
                positional_args.push(input.parse()?);
            }

            Ok(FormatArgs {
                format_string,
                positional_args,
                named_args,
            })
        }
    }

    // Extract the first argument, the format string literal, from an
    // invocation of a formatting or printing macro.
    fn get_format_string(m: &Macro) -> Result<LitStr> {
        let args: FormatArgs = m.parse_body()?;
        match args.format_string {
            Expr::Lit(ExprLit { lit: Lit::Str(lit), .. }) => Ok(lit),
            other => {
                // First argument was not a string literal expression.
                // Maybe something like: println!(concat!(...), ...)
                Err(Error::new_spanned(other, "format string must be a string literal"))
            }
        }
    }

    fn main() {
        let invocation = parse_quote! {
            println!("{:?}", Instant::now())
        };
        let lit = get_format_string(&invocation).unwrap();
        assert_eq!(lit.value(), "{:?}");
    }

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#### pub fn parse_body_with<F: Parser>(&self, parser: F) -> Result<F::Output>

Parse the tokens within the macro invocation’s delimiters using the given parser.

## Trait Implementations

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### impl Clone for Macro

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

Returns a copy of the value. Read more

1.0.0 · source

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

Performs copy-assignment from `source`. Read more

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### impl Parse for Macro

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

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### impl ToTokens for Macro

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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

Convert `self` directly into a `TokenStream` object. Read more

## Auto Trait Implementations

### impl RefUnwindSafe for Macro

### impl !Send for Macro

### impl !Sync for Macro

### impl Unpin for Macro

### impl UnwindSafe for Macro

## 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,

const: unstable · source

#### 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,

const: unstable · source

#### 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

const: unstable · source

#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T where
U: From<T>,

const: unstable · source

#### 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. Read more

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### impl<T> ToOwned for T where
T: Clone,

#### 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>,

#### type Error = Infallible

The type returned in the event of a conversion error.

const: unstable · source

#### 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>,

#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

const: unstable · source

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

Performs the conversion.