[performance] Show trait #2433
Description
motivation
Now that the show trait uses the &Logger trait object, using dynamic dispatch results in much worse performance than using StringBuilder directly.
///|
test "hello" {
if @lib.hello() != "Hello, world!" {
fail("@lib.hello() != \"Hello, world!\"")
}
}
///|
test (b : @bench.T) {
b.bench(name="StringBuilder", fn() {
let sb : StringBuilder = StringBuilder::new()
for _ in 0..<1000 {
sb.write_char('a')
}
})
b.bench(name="&Logger", fn() {
let lg : &Logger = StringBuilder::new()
for _ in 0..<1000 {
lg.write_char('a')
}
})
}
bench username/hello/lib/hello_test.mbt::1
name time (mean ± σ) range (min … max)
StringBuilder 14.62 µs ± 0.17 µs 14.38 µs … 14.85 µs in 10 × 6928 runs
&Logger 18.64 µs ± 0.19 µs 18.41 µs … 18.93 µs in 10 × 5365 runs
Total tests: 1, passed: 1, failed: 0. [native]
bench username/hello/lib/hello_test.mbt::1
name time (mean ± σ) range (min … max)
StringBuilder 17.91 µs ± 0.22 µs 17.57 µs … 18.28 µs in 10 × 5436 runs
&Logger 24.10 µs ± 0.83 µs 23.51 µs … 26.35 µs in 10 × 4139 runs
Total tests: 1, passed: 1, failed: 0. [wasm]
current API
pub(open) trait Show {
output(Self, &Logger) -> Unit
to_string(Self) -> String = _
}expected API
Using a concrete type is better and simpler than using a trait object.
pub(open) trait Show {
output(Self, StringBuilder) -> Unit
to_string(Self) -> String = _
}alternative choice
Extending the capabilities of traits to support generic traits solves this problem.