TypeFunction example creatiing a conversion matrix

[Steven Schveighoffer]

On 10/1/20 9:53 AM, H. S. Teoh wrote:
> On Thu, Oct 01, 2020 at 12:27:23PM +0000, Stefan Koch via Digitalmars-d wrote:
> [...]
>> type functions do a Type -> TypeObject conversion when you pass the
>> types in.
>> inside the type function you get a "type-like" interface.
>> But it has lost everything that made it a type.
>> It has sizeof, alignof, stringof, tupleof, you can use __traits on it.
>> But it cannot be used as a type anymore.
>> Not inside a type-function anyway.
>>
>> If you return a type or a type tuple from a type function, it becomes
>> a regular type/type tuple again.
> 
> Isn't this just the same thing as Andrei's reification / dereification,
> except redressed in terms of aliases?

The difference I see is that reification/dereification has to rebuild 
everything that is already in the compiler, but at runtime. And it has 
to make sure the functionality is identical. You are using the compiler 
to build another type introspection system, but just so you can do CTFE 
based things.

It reminds me of "modern" web applications which take over browser 
functionality (page navigation, etc.) and reimplement it in javascript.

If we can't get a system that allows dereifcation DURING function 
execution, then I think type functions are a much better solution. 
There's no reason to reimplement what the compiler already does. Type 
functions are cleaner, clearer, and much more efficient.

-Steve