On type functions

[Stefan Koch]

On Sunday, 3 May 2020 at 11:19:23 UTC, Panke wrote:
> On Sunday, 3 May 2020 at 11:11:03 UTC, Stefan Koch wrote:
>>
>> struct from spec is exactly one of the things that will not be 
>> possible without wrapping it in a template.
>>
>> template structFromString(string spec)
>> {
>>     alias structFromStringTypeFn(string spec)
>>     {
>>         ...
>>     }
>>     alias = structFromString = structFromStringTypeFn!(spec);
>> }
>> that looks a bit strange but it allows me to not have to worry 
>> about certain constraints that I would otherwise have to worry 
>> about.
>
> I have no problem with wrapping it in a template, but want to 
> know what can be done inside of structFromStringTypeFn?

You can not create ast-fragments or anything like that but you 
can create a string
which when mixed in within the scope of the wrapping template 
creates the type you want.

so structFromStringTypeFn would return a string rather than a 
type.
The only special thing in a type function is that you can use the 
usual `__traits` and tupleof, on the type parameter.
The rest is just like a regular function at ctfe.