Am Mittwoch, den 17.10.2018, 13:30 +0100 schrieb Richard Sandiford: > [ Sorry that there were so many typos in my last reply, will try to > do better > this time... ]
... > I think the key difference between sizeless types and full C99-style > VLAs is that the size and layout of sizeless types never matters for > semantic analysis. Rather than the sizes of types becoming variable > (and the offsets of members becoming variable, and constexprs > becoming > variable-sized, etc.), we simply don't make those concepts available > for sizeless types. > > So nothing at the language level becomes variable that was constant > before. > All that happens is that some things become invalid for sizeless > types > that would be valid for sized ones. > > The idea was really for the language to provide a framework for > implementations to define implementation-specific types with > implementation-specific rules while disturbing the language itself > as little as possible. I guess this makes it much easier for C++, but also much less useful. Surely, the processor knows the size when it computes using these types, so one could make it available using 'sizeof'. If a value of the type is stores in addressable memory (on the stack), can't we also store the size so that it is available for other threads? Just making it undefined to access a variable with the wong size for the current thread seems rather fragile to me. Best, Martin
