Re: How is std.traits.isInstanceOf supposed to work?

[TheFlyingFiddle]

The docs might be a little unclear about this. The template 
isInstanceOf checks to see if the second parameter is a template 
instantiation of the first parameter. It does not have anything 
to do with inheritance.

Like so:
struct S(T) { T t; }

struct S2(T) { T t; }

import std.traits;
unittest
{
    alias inst  = S!(int);
    alias inst2 = S2!(string);

    //S!(int) is an instantiation of S
    static assert(isInstanceOf!(S, inst));
    //S2!(string) is not an instantiation of S
    static assert(!isInstanceOf!(S, inst2));
}

If you would like to see if something is derived from something 
or to see if a struct is convertible to another struct use the is 
keyword.

Like so:


struct S3
{
    S!(int) s;
    alias s this;
}

class C { }

class D : C { }

unittest
{       
    //S3 is convertible to S!(int)
    static assert(is(S3 : S!(int)));
        
    //D is convertible (derived from) C
    static assert(is(D : C));
}