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There are some traits that can not be implemented within the current C++ language: to make these traits "just work" with user defined types, some kind of additional help from the compiler is required. Currently (May 2005) MWCW 9 and Visual C++ 8 provide the necessary intrinsics, and other compilers will no doubt follow in due course.
The Following traits classes always need compiler support to do the right thing for all types (but all have safe fallback positions if this support is unavailable):
The following traits classes can't be portably implemented in the C++ language, although in practice, the implementations do in fact do the right thing on all the compilers we know about:
The following traits classes are dependent on one or more of the above:
The hooks for compiler-intrinsic support are defined in boost/type_traits/intrinsics.hpp, adding support for new compilers is simply a matter of defining one of more of the following macros:
| BOOST_IS_UNION(T) | Should evaluate to true if T is a union type |
|---|---|
| BOOST_IS_POD(T) | Should evaluate to true if T is a POD type |
| BOOST_IS_EMPTY(T) | Should evaluate to true if T is an empty struct or union |
| BOOST_HAS_TRIVIAL_CONSTRUCTOR(T) | Should evaluate to true if the default constructor for T is trivial (i.e. has no effect) |
| BOOST_HAS_TRIVIAL_COPY(T) | Should evaluate to true if T has a trivial copy constructor (and can therefore be replaced by a call to memcpy) |
| BOOST_HAS_TRIVIAL_ASSIGN(T) | Should evaluate to true if T has a trivial assignment operator (and can therefore be replaced by a call to memcpy) |
| BOOST_HAS_TRIVIAL_DESTRUCTOR(T) | Should evaluate to true if T has a trivial destructor (i.e. ~T() has no effect) |
| BOOST_HAS_NOTHROW_CONSTRUCTOR(T) | Should evaluate to true if T x; can not throw |
| BOOST_HAS_NOTHROW_COPY(T) | Should evaluate to true if T(t) can not throw |
| BOOST_HAS_NOTHROW_ASSIGN(T) | Should evaluate to true if T t, u; t = u can not throw |
| BOOST_HAS_VIRTUAL_DESTRUCTOR(T) | Should evaluate to true T has a virtual destructor |
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