nom::opt!
[−]
[src]
macro_rules! opt { ($i:expr, $submac:ident!( $($args:tt)* )) => { ... }; ($i:expr, $f:expr) => { ... }; }
opt!(I -> IResult<I,O>) => I -> IResult<I, Option<O>>
make the underlying parser optional
returns an Option of the returned type. This parser never fails
named!( o<&[u8], Option<&[u8]> >, opt!( tag!( "abcd" ) ) ); let a = b"abcdef"; let b = b"bcdefg"; assert_eq!(o(&a[..]), Done(&b"ef"[..], Some(&b"abcd"[..]))); assert_eq!(o(&b[..]), Done(&b"bcdefg"[..], None));