"Error: `TypeInfo` cannot be used with -betterC" on a CTFE function

[Steven Schveighoffer]

On Tuesday, 9 April 2024 at 23:50:36 UTC, Richard (Rikki) Andrew 
Cattermole wrote:
> On 10/04/2024 11:21 AM, Liam McGillivray wrote:
>> On Sunday, 7 April 2024 at 08:59:55 UTC, Richard (Rikki) 
>> Andrew Cattermole wrote:
>>> Unfortunately runtime and CTFE are the same target in the 
>>> compiler.
>>>
>>> So that function is being used for both, and hence uses GC 
>>> (appending).
>> 
>> Are you sure that string appending was really the problem that 
>> caused the "TypeInfo" build error? I forgot about this, but I 
>> had already had a working CTFE function with string appending 
>> before adding the new one that lead to this error. The symbols 
>> that it generates could be used in the program compiled with 
>> `betterC`.
>
> No, for a string it shouldn't trigger the need for TypeInfo. 
> But that wouldn't have worked regardless.

Array appending calls a runtime function which accepts `TypeInfo` 
(In this case, `TypeInfoGeneric!char`). So this does indeed 
involve `TypeInfo`. But also, even if `TypeInfo` weren't 
involved, it also needs the GC which is unavailable with betterC. 
It's just that the `TypeInfo` error happens first.

The move to use templates instead of `TypeInfo` is slowly 
happening.

-Steve