Remove the need for a callback to be passed to format_args! #20136
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eddyb
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This looks amazing @eddyb, really nice work! This is a somewhat-large structure to be passing around by value, could you make sure we're not giving up any perf with a benchmark or two? |
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So I ended up on a wild goose chase. Or to be more precise, chasing the ghosts of nanoseconds. Turns out we generate the same IR - technically it differs, but only in ordering of the instructions. |
…g a wrapper block.
…ing a function with them.
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Thanks for investigating this @eddyb! I'm excited for this to land! |
We have the technology: no longer do you need to write closures to use `format_args!`.
This is a `[breaking-change]`, as it forces you to clean up old hacks - if you had code like this:
```rust
format_args!(fmt::format, "{} {} {}", a, b, c)
format_args!(|args| { w.write_fmt(args) }, "{} {} {}", x, y, z)
```
change it to this:
```rust
fmt::format(format_args!("{} {} {}", a, b, c))
w.write_fmt(format_args!("{} {} {}", x, y, z))
```
To allow them to be called with `format_args!(...)` directly, several functions were modified to
take `fmt::Arguments` by value instead of by reference. Also, `fmt::Arguments` derives `Copy`
now in order to preserve all usecases that were previously possible.
We have the technology: no longer do you need to write closures to use
format_args!.This is a
[breaking-change], as it forces you to clean up old hacks - if you had code like this:change it to this:
To allow them to be called with
format_args!(...)directly, several functions were modified totake
fmt::Argumentsby value instead of by reference. Also,fmt::ArgumentsderivesCopynow in order to preserve all usecases that were previously possible.