Simple command-line app to investigate the performance tradeoffs between different methods of copying and mutating a struct.
I started with the assumption that using a nonescaping closure that accepted an inout value would be measurably slower than an old-school copy and assign. Swift closures generally have overhead in capturing values, and inout by default are copied in and out of their execution context. This should add up to a measurable performance penalty vs directly manipulating stack-local variables.
On my MacBook Pro (M1 Pro), the results were:
1.0694s : copy and assign
0.6949s : Mutate
0.5799s : Mutate with struct creation in loop
0.6929s : Mutate Unsafe
3.4349s : copy and assign w/ for-in loop
0.8210s : assign with no copy
0.5683s : Mutate with no copy
- Clang is very, very smart
- The largest performance impact of the various methods I tried was actually in using a
for-inloop structure instead of awhile - Closures were actually faster in most cases, for reasons I can't fathom
- None of this matters unless you're in a hot inner loop of performance-critical code. For 99.9% of cases, choose what's syntactically clear.
- Don't try to outsmart the compiler.