C++ Type Traits

Question

I understand they encode information about the type you instantiate them with, but how do they work? Say, for instance, the type trait std::is_class. How d

Answer 1

Some type traits, like std::is_class just use compiler intrinsics (aka built-ins). You cannot write these yourself without special support from the compiler.

Type traits are mostly useful in generic context—you may want to specialize things based on the properties of types, or impose restrictions on template arguments. For example, an implementation of std::copy may use std::memcpy internally instead of an explicit loop when the iterators are pointers to PODs. This can be achieved with SFINAE.