AW: [std-proposals] Make all data pointers intercompatible

>> No, not "only". An implementation that e.g. >masks out the

>> least>significant bits of void* on conversion to T*, >according to
>> T's>alignment requirements, is possible. This will violate the strict
>> aliasing rule. And any type can alias any type.

>I don't see how that would violate the strict >aliasing rule, as it only
>concerns valid pointers. Pointers that do not >respect pointed object
>alignment are not valid.

As per your example, if you correct the alignment when converting from void* => T*, why not generalize it for all T* <=> U*, and eliminate the extra T*=>void* before going from void*=>U*.

>>> Another implementation that e.g.>modifies tag bits in the pointer according
>>> to T >(e.g. to distinguish>between pointed types in hardware to >improve
>>> security) is also possible.This is counter intuitive, because you will get
>>> a page of unsecured memory with some cells tagged as secured, or the
>>> opposite which is worse.Manipulating bits of a pointer should be a
>>> programmer responsibility, not the implementation.

>A programmer does not have the standard >means to manipulate bits in a
>pointer representation while maintaining >pointer validity. Manipulating
>object (including pointer) representation is >the responsibility of the
>compiler.

The compiler gives you a general purpose fundamental type, and you can customize it to your liking.

>>> Can you point where this is specified in the >standard?In the definition of
>>> the pointer type itself as a fundamental type.

I don't see where.

>> a pointer as a type defines 5 operations:++ increment , -- decrement ,
>> +ptr_diff_t add an offset, * dereference, (T*) castingNone manipulate bits.

>The list of supported operations on pointers >is irrelevant. This is just
>the model that the language provides to >users. It doesn't mean that an
>implementation can't manipulate bits of >pointer representation using any
>instructions it sees fit.

But that model reflects the underlying hardware. No need to abstract it away from the programmer.

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