Use null-coalescing assignment where applicable

[BCSharp]

This is for both performance and readability improvements.

[slozier]

I guess this is adding an extra null check so not quite equivalent. Was this intentional?

[BCSharp]

Thanks for paying attention 😄 (there are a lot of changes), but yes, it was intentional, for readability.

I also thought it would be better performance-wise, but after closer examination of the generated IL code it turns out that the performance is better in Debug (unoptimized) configuration but worse in Release (optimized).

So I will fix it in the next commit.

Here is some background info. Considering the code path when _alias is already not null.

if (_alias == null) {
    _alias = lambda.Name;
    _alias ??= "$lambda" + ++_lambdaId;
}

generates normally

IL_0001	ldarg.0	
IL_0002	ldnull	
IL_0003	ceq	
IL_0005	stloc.0	
IL_0006	ldloc.0	
IL_0007	brfalse.s	IL_0039
...
IL_0039	ret	

But when optimized:

IL_0000	ldarg.0	
IL_0001	brtrue.s	IL_0031
...
IL_0031	ret	

Code:

_alias ??= lambda.Name;
_alias ??= "$lambda" + ++_lambdaId;

generates in both release and debug:

IL_0001	ldarg.0	
IL_0002	brtrue.s	IL_000C
...
IL_000C	ldarg.0	
IL_000D	brtrue.s	IL_0032
...
IL_0032	ret	

[BCSharp]

Another option that wins in both Debug and Release:

_alias ??= lambda.Name ?? "$lambda" + ++_lambdaId;

[slozier]

Thanks!