Reimplementing the bulk of std.meta iteratively

[Timon Gehr]

On 01.10.20 10:56, Walter Bright wrote:
> On 10/1/2020 12:48 AM, Timon Gehr wrote:
>> (In terms of compiler implementation, the runtime representation of 
>> `T` would contain all information that is necessary to figure out 
>> calling conventions of functions that take a T, it would contain 
>> sizeof, pointers to destructor/postblit, etc, so basically it's typeid.)
> 
> I had looked into this. Unfortunately, many aspects of types are simply 
> too complex to try and represent at run time. For example, is type T1 
> implicitly convertible to T2? This seemingly simple question is very 
> complex. Yes, `alias this` makes it much worse :-/
> ...

The compiler can figure it out, so you *could* just put that logic into 
druntime. However, for first-class types, you don't need to check 
implicit conversions at run time, therefore this would not be necessary.

> I initially had high hopes for typeid back when it was originally 
> designed 20 years ago. It ably fulfills its original purpose of enabling 
> the GC and associative arrays in a language with no templates.
> ...

And a monomorphic type system.

> I don't see much future for it other than being kept around for legacy 
> compatibility.

I was explaining conditions for types to be "first-class". So unless 
that is a goal, typeid might not see a revival.