Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
For much of this library, there are two interfaces: one in namespace boost::stl_interfaces::v1, and
one in boost::stl_interfaces::v2. The v1
version uses SFINAE to constrain templates, and the v2
version uses concepts, including the standard concepts from C++20.
When you build with a conforming C++20 compiler, the compiler defines a macro
__cpp_lib_concepts that indicates
that the compiler supports concepts, and provides the standard concepts in
std and std::ranges.
When Boost.STLInterfaces sees the __cpp_lib_concepts
macro defined, it inlines the v2
namespace; otherwise, it inlines the v1
namespace.
The net result for you as a user is that, for some function or type foo with v1
and v2 versions, you can use
boost::stl_interfaces::foo, and you will get boost::stl_interfaces::v1::foo when building in C++14 or C++17 modes,
and boost::stl_interfaces::v2::foo
when building in C++20 or later.
If you are using an early C++20 implementation that claims to have concept
support, but that breaks when you build Boost.STLInterfaces's C++20 code, you
can disable the v2 namespace
by defining BOOST_STL_INTERFACES_DISABLE_CONCEPTS.
]