Struct syn::Macro

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

This is supported on crate features full or derive only.

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

impl Macro

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

This is supported on crate feature parsing only.

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(), "{:?}");
}

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

This is supported on crate feature parsing only.

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

Trait Implementations

impl Clone for Macro

This is supported on crate feature clone-impls only.

pub fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Macro

This is supported on crate feature extra-traits only.

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

Formats the value using the given formatter.

impl Eq for Macro

This is supported on crate feature extra-traits only.

impl Hash for Macro

This is supported on crate feature extra-traits only.

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

Feeds this value into the given Hasher.

pub fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given Hasher.

impl Parse for Macro

This is supported on crate feature parsing only.

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

impl PartialEq<Macro> for Macro

This is supported on crate feature extra-traits only.

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

This method tests for self and other values to be equal, and is used by ==.

#[must_use]pub fn ne(&self, other: &Rhs) -> bool

This method tests for !=.

impl ToTokens for Macro

This is supported on crate feature printing only.

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

Write self to the given TokenStream.

pub fn to_token_stream(&self) -> TokenStream

Convert self directly into a TokenStream object.

pub fn into_token_stream(self) -> TokenStream

Convert self directly into a TokenStream object.