Is C# 6 ?. (Elvis op) thread safe? If so, how?

Question

Apologies in advance: this question comes from a hard-core, unreformed C++ developer trying to learn advanced C#. Consider the following:

if (myUserDefinedOb         


        

Answer 1

From MSDN (emphasis mine):

Another use for the null-condition member access is invoking delegates in a thread-safe way with much less code. The old way requires code like the following:

var handler = this.PropertyChanged;
if (handler != null)
    handler(…)

The new way is much simpler:

PropertyChanged?.Invoke(e)

The new way is thread-safe because the compiler generates code to evaluate PropertyChanged one time only, keeping the result in temporary variable.

So there is no locking involved here - thread-safety is enforced by creating a local temporary variable, which prevents a different thread from modifying that variable in between the null check and some other operation.