[Proposal] Null-coalescing Assignment Operator: ??= #205
Description
??= would have semantics analogous to the existing compound assignment operators like +=, %=, and <<=. More precisely, x ??= y would be equivalent to x = x ?? y except that x is evaluated only once. It would have clear, if not vast, utility. Hopefully, it would not be an unreasonably large effort.
It is perhaps debatable whether
object o = GetFirstChoice( foo, bar, someLongArgument )
?? GetSecondChoice( foo, bar, someLongArgument )
?? GetFallback();looks better than
object o = GetFirstChoice( foo, bar, someLongArgument );
o ??= GetSecondChoice( foo, bar, someLongArgument );
o ??= GetFallback();However, the latter seems easier to step through in the debugger.
Furthermore, a use case like
private static void ApplyNewSettings( SettingsSource newSource ) {
// Set each setting if and only if it is not already set to a non-null value.
// This could be e.g. applying defaults after deserializing user settings.
this.SomeSetting ??= newSource.SomeSetting;
// ...
}is less repetitive with ??=.