Re: Extracting string parameter from template instance received via alias parameter

[anonymous via Digitalmars-d]

On Friday, 12 September 2014 at 19:44:28 UTC, MrSmith wrote:

Given the following program:

---------------------------------
import std.stdio;

template first(string s)
{
        string first(string par)
        {
                if (par == s)
                        return "true";
                else
                        return "false";
        }
}

template second(alias firstInstance)
{
        string second(string par)
        {
                // this line doesn't work
                static if (is(firstInstance : F!(str), alias F, string str))

`is(...)` checks for types. firstInstance isn't a type, it's a
function, so the `is` expression is always false. You can use
std.traits.TemplateArgsOf instead:

                 import std.traits;
                 import std.typetuple;
                 static if(__traits(compiles,
TemplateArgsOf!firstInstance))
                 {
                     alias targs = TemplateArgsOf!firstInstance;
                     static if(is(typeof(targs) ==
TypeTuple!string))
                         writeln("matched ", targs[0]);
                 }

                {
                        writeln("matched ", str);
                }
                
                enum s = "XXX"; // get s from firstInstance
                // without parsing strings and using mixins

// something like second(alias C : F!(str), alias F, string str)

You're on the right track:

template second(alias C : F!(str), alias F, string str)
{
         string second(string par)
         {
                 import std.string : icmp;
                 if (icmp(par, str) == 0)
                         return "true";
                 else
                         return "false";
         }
}
        

                import std.string : icmp;
                if (icmp(par, s) == 0)
                        return "true";
                else
                        return "false";
        }
}

void main()
{
        writeln(first!"str"("str"));

writeln(second!( first!"str" )("StR")); // should match string from first, but case insensetive

}

---------------------------------

How do I extract s parameter of first passed to second via alias parameter. It seems like it is not possible. Or is it?