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16.2.8 The typename Keyword
The typename keyword was added to C++ after the initial
specification and is not recognized by all compilers. It is a hint to
the compiler that a name following the keyword is the name of a type.
In the usual case, the compiler has sufficient context to know that a
symbol is a defined type, as it must have been encountered earlier in
the compilation:
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class Foo
{
public:
typedef int map_t;
};
void
func ()
{
Foo::map_t m;
}
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Here, map_t is a type defined in class Foo . However, if
func happened to be a function template, the class which contains
the map_t type may be a template parameter. In this case, the
compiler simply needs to be guided by qualifying T::map_t as a
type name:
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class Foo
{
public:
typedef int map_t;
};
template <typename T>
void func ()
{
typename T::map_t t;
}
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