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perf: improve write_fmt to handle simple strings In case format string has no arguments, simplify its implementation with a direct call to `output.write_str(value)`. This builds on `@dtolnay` original [suggestion](https://github.com/serde-rs/serde/pull/2697#issuecomment-1940376414). This does not change any expectations because the original `fn write()` implementation calls `write_str` for parts of the format string. ```rust write!(f, "text") -> f.write_str("text") ``` ```diff /// [`write!`]: crate::write! +#[inline] #[stable(feature = "rust1", since = "1.0.0")] pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result { + if let Some(s) = args.as_str() { output.write_str(s) } else { write_internal(output, args) } +} + +/// Actual implementation of the [`write`], but without the simple string optimization. +fn write_internal(output: &mut dyn Write, args: Arguments<'_>) -> Result { let mut formatter = Formatter::new(output); let mut idx = 0; ``` * Hopefully it will improve the simple case for the https://github.com/rust-lang/rust/issues/99012 * Another related (original?) issues #10761 * Previous similar attempt to fix it by by `@Kobzol` #100700 CC: `@m-ou-se` as probably the biggest expert in everything `format!` |
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