empty string vs. null string

[kasperk81]

s += null;

gets compiled to s ?? ""

s += string.Empty;

gets compiled to a method call s = string.Concat(s, string.Empty). can it be s ?? "" as well?

[jaredpar]

can it be s ?? "" as well?

Possibly but is there a specific benefit of doing that? Does it shrink IL, have better throughput, etc ....

[kasperk81]

yes there is a codegen impact.
@EgorBo assuming runtime can't optimize this pattern?

[jaredpar]

Okay but how common is this pattern? Hard to see this being a big item we should be prioritizing.

[EgorBo]

yes there is a codegen impact. @EgorBo assuming runtime can't optimize this pattern?

I think we can tweak the JIT's inliner a bit to optimize this case, here it's not optimized because String.Concat is not inlined

[kasperk81]

if it can be handled in runtime, i will close this. something i noticed in a pr review somewhere that preference was to use string.Empty in new dotnet versions because "there is no difference in perf", then i found this call which broke that assumption.