Re: Allowing "fall through" of attributes

[Lodovico Giaretta via Digitalmars-d-learn]

On Tuesday, 19 July 2016 at 15:55:02 UTC, Rufus Smith wrote:
I have some functions that take other functions. I would like 
the attributes to be able to "fall" through so I get overload 
like behavior. I only care that I am passing a function, not if 
it is shared, extern(C), pure, @nogc, etc.

void foo(R, A...)(R function(A) bar)
{
   alias type = typeof(bar);
   pragma(msg, type);
   // does magic with bar
}

foo never uses the attributes of bar explicitly. It uses type 
to instantiate other functions like bar. I have to create a foo 
for each attribute combination, which is not worth while. The 
code seems to break only for extern, the best I can tell, most 
attributes do pass through. But type does not contain these 
attributes.

You shall do something like this (please note that I didn't check 
the docs while writing this; you shall definitely have a look at 
std.traits and consider the following as pseudo-code and not 
actual D):

void foo(Fun)(Fun bar)
    if (isSomeFunction!Fun)   // your constraint that bar is a 
function
{
    // how to get your R and A types, if you need them:
    alias R = ReturnType!bar;
    alias A = Parameters!bar;

    alias type = Fun;
    pragma(msg, type);

    // do some magic
}