Proposal: Null-conditional Assignment (Lazy Initialization Operator)

[alrz]

Currenty (no concurrency check):

public Foo Foo => _foo ?? (_foo = new Foo());

Null-conditional Assignment:

public Foo Foo => _foo ?= new Foo();

This can be implemented in a way that properly use the System.Threading.LazyInitializer class.

[HaloFour]

Dupe of #3366.

[alrz]

@HaloFour Sorry I didn't see it, since it's closed. They didn't mention LazyInitializer though, nor the use case I suggested here.

[HaloFour]

Well there is #3630 specifically for lazy initialization using a decorator on property signatures. Using the operator syntax makes it feel like it is much more general purpose. The fact that it could be used to emulate lazy behaviors in properties I don't think matters much, and if it would behave differently than a null assignment in that context I think that would make it confusing.

[alrz]

@HaloFour Lazy initialization is not bounded to properties. you still want to use it in other places. what about initializing a private field in some method? It is general purpose. you can use them everywhere for initializing members. and it just works — thread safely.

[alrz]

This is neatly covered by replace/original feature.

public class Foo {
  [Lazy]
  public object Value => GetValue();
}

partial class Foo {
  object mValue;
  replace object Value => mValue ?? (mValue = original);
}

Thread safety and other stuff is up to the code gen provider.