The ValueType parameter of std::any_cast is confusingly named

[jwakely]

template<class ValueType>
  ValueType any_cast(const any& operand);
template<class ValueType>
  ValueType any_cast(any& operand);
template<class ValueType>
  ValueType any_cast(any&& operand);

This template parameter is confusing, because it's really the return type of the function, not the type of the contained value in the any (as shown by the fact the requirements say it must be a reference, or copy constructible). When the parameter is a reference the functions return by reference, not by value, and ValueType is not the type of the value in the any. The parameter can be const but the value in the any is not a const-qualified type.

Elsewhere in the library "value type" is used for containers, iterators, and allocators, and must be an object type, not a reference type.

I suggest renaming this to make it clearer that it can be a reference, and is not the type of the value in the any. Result or ResultType might be better. Or just Type or T.

For the any_cast overloads taking pointers the ValueType parameter is OK, as in that case it does refer to the type of the value in the any.

[timsong-cpp]

any's member functions (ctor, =, emplace) have similar problems. The actual type of the value being stored is the decayed type, not actually ValueType, despite the name.

The pointer variant of any_cast also has issues - ValueType can be cv-qualified (the comparison is by typeid which drops cv-qualification), but the value being stored is not.

[jensmaurer]

I'm preparing a patch that replaces ValueType with T and uses VT where the description seems to hint we're dealing with the actual ValueType.

[jwakely]

That sounds good to me - thanks.