rtti: missing sizeof() and alignof() in std::type_info

[Matthew Fioravante]

Is there any reason that sizeof(T) and alignof(T) are not available via the type_info struct from typeid()?

I want to use the address and size in particular to create a mapping of objects within other objects for debugging purposes. It doesn't actually appear to be possible in C++14 to get the size of the most dynamic type without rolling your own rtti solution.

What I would suggest is adding size() and align() methods to type_info to return sizeof(T) and alignof(T) respectively.

[Nicol Bolas]

I wouldn't suggest calling it `size`, as that term is generally reserved for getting the number of elements in a container object. If we add a global `size` function that will call member `size` functions (assuming C++17 doesn't give us the ability to call member functions as if they were global), you wouldn't want `type_info` to respond to such a function call.

Perhaps `size_of` and `align_of`.

[Andrey Semashev]

<bikeshed_mode>'object_size' and 'alignment'?</bikeshed_mode>

An interesting idea at the first glance, this would probably increase
type_info size overhead whether these functions are used or not, and I
expect them to be used rarely. Not sure this is worth it, provided
that an opt-in solution is possible.

[Thiago Macieira]

Sounds like a reasonable proposal, but one tricky to implement.

In order to support polymorphic types linked before this feature, it needs to
support returning sizeOf() == alignOf() == 0 or another sentinel value that
indicates absence of information.

Also note that typeid(void) is valid, so what does typeid(void).sizeOf()
return?
--
Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
Software Architect - Intel Open Source Technology Center
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