How to get value of type at CT given only an alias

[Steven Schveighoffer via Digitalmars-d-learn]

On 7/14/17 1:51 PM, FoxyBrown wrote:
> Trying to do some tricky stuff but I can't seem to get the value of a 
> type(enum in my case, but must work in general).
> 
> Basically, given a type T or an alias T(alias preferred), I'd like to be 
> able to get the "default value" of that type.
> 
> e.g.,
> 
> if it is an enum and I have an alias to a member, instead of (Enum)3 I 
> want 3.
> 
> if it is a member field, I want the default value.
> 
> if it is a function pointer, the address(probably 0, but whatever).
> 
> Basically a sort of generic "getValue" that attempts to get the CT value 
> of any type, if it exists. (obviously the value of class is meaningless, 
> so returns ""... class isn't even a type, but can still query).
> 
> In fact, I'd like to also naturally resolve the value back in to the 
> expression that created it.
> 
> e.g.,
> 
> (Enum)3 -> Enum.ThirdEntry
> 
> 

.init is the default value.

I'm not sure you can get the default value of a non-default initializer, 
My attempts using init didn't work. e.g.:

void foo(alias T)()
{
    pragma(msg, T.init);
}

struct S
{
    int y = 5;
    void bar() { foo!y; } // prints 0
}

-Steve