TypeFunction example creatiing a conversion matrix

[Stefan Koch]

On Thursday, 1 October 2020 at 19:33:09 UTC, Andrei Alexandrescu 
wrote:

>
> A proof of concept would be helpful.

You mean this one:

template ImplicitConversionTargets(T)
{
     static if (is(T == bool))
         alias ImplicitConversionTargets =
             AliasSeq!(byte, ubyte, short, ushort, int, uint, 
long, ulong, CentTypeList,
                        float, double, real, char, wchar, dchar);
     else static if (is(T == byte))
         alias ImplicitConversionTargets =
             AliasSeq!(short, ushort, int, uint, long, ulong, 
CentTypeList,
                        float, double, real, char, wchar, dchar);
     else static if (is(T == ubyte))
         alias ImplicitConversionTargets =
             AliasSeq!(short, ushort, int, uint, long, ulong, 
CentTypeList,
                        float, double, real, char, wchar, dchar);
     else static if (is(T == short))
         alias ImplicitConversionTargets =
             AliasSeq!(int, uint, long, ulong, CentTypeList, 
float, double, real);
     else static if (is(T == ushort))
         alias ImplicitConversionTargets =
             AliasSeq!(int, uint, long, ulong, CentTypeList, 
float, double, real);
     else static if (is(T == int))
         alias ImplicitConversionTargets =
             AliasSeq!(long, ulong, CentTypeList, float, double, 
real);
     else static if (is(T == uint))
         alias ImplicitConversionTargets =
             AliasSeq!(long, ulong, CentTypeList, float, double, 
real);
     else static if (is(T == long))
         alias ImplicitConversionTargets = AliasSeq!(float, 
double, real);
     else static if (is(T == ulong))
         alias ImplicitConversionTargets = AliasSeq!(float, 
double, real);
     else static if (is(cent) && is(T == cent))
         alias ImplicitConversionTargets = AliasSeq!(float, 
double, real);
     else static if (is(ucent) && is(T == ucent))
         alias ImplicitConversionTargets = AliasSeq!(float, 
double, real);
     else static if (is(T == float))
         alias ImplicitConversionTargets = AliasSeq!(double, real);
     else static if (is(T == double))
         alias ImplicitConversionTargets = AliasSeq!real;
     else static if (is(T == char))
         alias ImplicitConversionTargets =
             AliasSeq!(wchar, dchar, byte, ubyte, short, ushort,
                        int, uint, long, ulong, CentTypeList, 
float, double, real);
     else static if (is(T == wchar))
         alias ImplicitConversionTargets =
             AliasSeq!(dchar, short, ushort, int, uint, long, 
ulong, CentTypeList,
                        float, double, real);
     else static if (is(T == dchar))
         alias ImplicitConversionTargets =
             AliasSeq!(int, uint, long, ulong, CentTypeList, 
float, double, real);
     else static if (is(T : typeof(null)))
         alias ImplicitConversionTargets = AliasSeq!(typeof(null));
     else static if (is(T == class))
         alias ImplicitConversionTargets = 
staticMap!(ApplyLeft!(CopyConstness, T), 
TransitiveBaseTypeTuple!(T));
     else static if (isDynamicArray!T && !is(typeof(T.init[0]) == 
const))
     {
        static if (is(typeof(T.init[0]) == shared))
            alias ImplicitConversionTargets =
            AliasSeq!(const(shared(Unqual!(typeof(T.init[0]))))[]);
        else
            alias ImplicitConversionTargets =
            AliasSeq!(const(Unqual!(typeof(T.init[0])))[]);
     }
     else static if (is(T : void*))
         alias ImplicitConversionTargets = AliasSeq!(void*);
     else
         alias ImplicitConversionTargets = AliasSeq!();
}

@Andrei could you explain the semantics in detail?
The source code is somewhat obtuse.