Programmatic type construction with @infoType

[marler8997]

The ability to modify/infer types from other types is a key feature of generic programming. It is proposed that the langauge add support to programmitcally create types from comptime TypeInfo structs with the @infoType function, i.e.

assert(u8 == @infoType(@import("builtin").TypeInfo.Int { .is_signed = false, .bits = 8, }));

@infoType is the inverse of the @typeInfo function and it's signature would be:

@infoType(comptime info: @import("builtin").TypeInfo) type

The following comment describes how this feature can be used to implement the SliceType and ArrayPointerType functions which take an array/pointer type and return either the slice or array pointer variation of it while preserving the const/volatile/allowzero properties:

#2782 (comment)

The point being that without programmatic generation of types, the code requires 2^N cases to return a type where N is the number of properties for that type (i.e. const/volatile/allowzero). See the comment in the above link for further clarification.

[andrewrk]

This is #383