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perf: improve write_fmt to handle simple strings

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Per @dtolnay suggestion in https://github.com/serde-rs/serde/pull/2697#issuecomment-1940376414 - attempt to speed up performance in the cases of a simple string format without arguments:

```rust
write!(f, "text")  ->  f.write_str("text")
```
This commit is contained in:
Yuri Astrakhan 2024-02-12 23:44:28 -05:00
parent 0b9f6ad994
commit d712e3f4f4
1 changed files with 6 additions and 4 deletions
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10
library/core/src/fmt/mod.rs
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@ -201,14 +201,14 @@ pub trait Write {
impl<W: Write + ?Sized> SpecWriteFmt for &mut W {
#[inline]
default fn spec_write_fmt(mut self, args: Arguments<'_>) -> Result {
write(&mut self, args)
if let Some(s) = args.as_str() { self.write_str(s) } else { write(&mut self, args) }
}
}
impl<W: Write> SpecWriteFmt for &mut W {
#[inline]
fn spec_write_fmt(self, args: Arguments<'_>) -> Result {
write(self, args)
if let Some(s) = args.as_str() { self.write_str(s) } else { write(self, args) }
}
}
@ -1582,8 +1582,9 @@ impl<'a> Formatter<'a> {
/// assert_eq!(format!("{:0>8}", Foo(2)), "Foo 2");
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result {
write(self.buf, fmt)
if let Some(s) = fmt.as_str() { self.buf.write_str(s) } else { write(self.buf, fmt) }
}
/// Flags for formatting
@ -2272,8 +2273,9 @@ impl Write for Formatter<'_> {
self.buf.write_char(c)
}
#[inline]
fn write_fmt(&mut self, args: Arguments<'_>) -> Result {
write(self.buf, args)
if let Some(s) = args.as_str() { self.buf.write_str(s) } else { write(self.buf, args) }
}
}