.d

import std.traits;
template polymorphic(alias F){
    auto polymorphic(T...)(T args){
        mixin((){
            import std.conv:to;
            string o;
            foreach(i,S;(Parameters!F)[0..T.length]){
                o~="args["~i.to!string~"].to!"~S.stringof~",";
            }
            return "return F("~o~");";
        }());
}}

void foo(int,float,bool=true){}
alias bar=polymorphic!foo;
struct myint{
    int i;
    int to(T:int)()=>i;
}
alias somefloat=double;
float to(T:float)(somefloat)=>float.init;

int add(int i,int j)=>i+j;
alias add_=polymorphic!add;
void main(){
    bar(myint(),somefloat.init);
    import std;
    int i=add_(myint(1),myint(2));
    i.writeln;
}