Array of templated classes or structs

[TheFlyingFiddle via Digitalmars-d-learn]

On Saturday, 24 October 2015 at 18:29:08 UTC, TheFlyingFiddle 
wrote:
> Variant[] array;
> array ~= S!int(...);
> array ~= S!double(...);
> array ~= S!long(...);
> array ~= "I am a string!";
>
> And this is probably not what you want.

You can do this if you want to ensure that items stored in the 
variant are of
a specific template struct/class.

import std.traits, std.variant;
struct TemplateStruct(alias template_)
{
    private Varint v;
    void opAssign(TemplateStruct!template_ other)
    {
        this.v = other.v;
    }

    void opAssing(T)(T t) if(isInstanceOf!(template_, T))
    {
        this.v = t;
    }

    T* peek(T) { return v.peek!T; }
    auto visit(Handlers...) { return v.visit!handler; }
    //More variant stuff here.
}


This should work: (untested)
TemplateStruct!(S)[] array;
array ~= S!int(...);
array ~= S!long(...);
array ~= S!double(...);
array ~= "I am a string!"; //This line should issue a compiler 
error.

To complete TemplateStruct simply forward the remaing members of 
the
variant. Or use something like proxy!T in std.typecons. Or use an 
alias this v.
(I don't really recommend alias this it has all kinds of problems)