On 8/29/21 3:31 PM, Charles Hixson wrote:
> Thanks. I going to have to study:
>
> enum supportsCall = isIntegral!(typeof(T.init.%s()));
>
>
> for awhile to make any sense of that, but it looks like just what I was
> looking for.
Trying to explain with comments:
// This is an eponymous template because it contains
// a symbol that's the same as the name of this template.
// And that symbol is 'supportsCall'. So, this template
// will be whatever that symbol is. (In this case, it
// will be a compile-time know entity: 'enum bool'.)
template supportsCall(T, string func) {
import std.format : format;
import std.traits : isIntegral;
// This is a string expression we will mix-in below.
enum expr = format!q{
enum supportsCall = isIntegral!(typeof(T.init.%s()));
}(func);
// The above expression will be the following e.g.
// for 'int' and for "ndx":
//
// enum supportsCall = isIntegral!(typeof(int.init.ndx()));
//
// So, it's determining whether the typeof the expression
// int.init.ndx() is an integral.
//
// 'supportsCall' is a bool, which I could have made explicit:
//
// enum bool supportsCall = [...]
//
// You can prove it for yourself by "printing" the expression
// at compile time:
pragma(msg, expr);
// Here is where we mix-in the expression into this template's
// definition.
mixin (expr);
}
Then the whole template can be used as a compile-time bool value.
Ali
