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Github impl FromStr for proc_macro::Literal by dtolnay · Pull Request #84717 · r...

 3 years ago
source link: https://github.com/rust-lang/rust/pull/84717
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dtolnay commented 8 days ago

Note that unlike impl FromStr for proc_macro::TokenStream, this impl does not permit whitespace or comments. The input string must consist of nothing but your literal.

  • "1".parse::<Literal>() ⟶ ok

  • "1.0".parse::<Literal>() ⟶ ok

  • "'a'".parse::<Literal>() ⟶ ok

  • "\"\n\"".parse::<Literal>() ⟶ ok

  • "0 1".parse::<Literal>() ⟶ LexError

  • " 0".parse::<Literal>() ⟶ LexError

  • "0 ".parse::<Literal>() ⟶ LexError

  • "/* comment */0".parse::<Literal>() ⟶ LexError

  • "0/* comment */".parse::<Literal>() ⟶ LexError

  • "0// comment".parse::<Literal>() ⟶ LexError

Use case

let hex_int: Literal = format!("0x{:x}", int).parse().unwrap();

The only way this is expressible in the current API is significantly worse.

let hex_int = match format!("0x{:x}", int)
    .parse::<TokenStream>()
    .unwrap()
    .into_iter()
    .next()
    .unwrap()
{
    TokenTree::Literal(literal) => literal,
    _ => unreachable!(),
};

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