'is(T==return)' How does is expression with return keyword as TypeSpecialization

[Steven Schveighoffer]

On 7/5/18 6:32 AM, Timoses wrote:
>      int fun(T)(T i)
>      {
>          static assert(is(typeof(return) == T)); //true

This is the type of the return value for the function you are in.

>          pragma(msg, is(T == return)); // false

This is not a valid is expression, which is why it's false. IMO, I think 
this should be an error.

Only is(T == struct), is(T == class), etc. works.

>          static if (is(T ReturnType == return))

As you have surmised, if T is a function, function pointer, or delegate, 
then it evaluates to true, and ReturnType is set to the return type of 
that function. Note, it has nothing to do with the function you are in, 
unlike typeof(return).

-Steve