Champion "Null-coalescing assignments" (16.3, Core 3)

[MadsTorgersen]

Introduces ??=.

Note: a minor change to ?? is included in this feature as implemented, so that it allows unconstrained type parameter types on the left.

• Proposal added: proposals/null-coalecing-assignment.md
• Discussed in LDM
• Decision in LDM
• Finalized (done, rejected, inactive)
• Spec'ed

LDM history:

• https://github.com/dotnet/csharplang/blob/master/meetings/2019/LDM-2019-04-15.md (result type)

[MgSam]

Glad to see this feature graduated from the "we will never do this!" bucket. :)

[Thaina]

Should we also support &&= and ||= operators?

Yes please

[devinvisible]

Very excited for this! Nice syntactic sugar similar to Ruby's ||=

[paulomorgado]

@Thaina, what are the use cases for &&= and ||=.

[Thaina]

@paulomorgado

var mustAllTrue = Condition0;
mustAllTrue &&= Condition1;
mustAllTrue &&= Condition2;

[CyrusNajmabadi]

@Thaina You can already do that today with:

var mustAllTrue = Condition0;
mustAllTrue &= Condition1;
mustAllTrue &= Condition2;

[yaakov-h]

@CyrusNajmabadi Wouldn't that still unconditionally evaluate the right-hand side? I'd expect in a situation such as:

var val = true;
val &&= BigExpensiveOperationReturningBool();

that BigExpensiveOperationReturningBool is not executed.

[CyrusNajmabadi]

@CyrusNajmabadi Wouldn't that still unconditionally evaluate the right-hand side?

Ah, point taken.