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A metafunction class is a certain form of metafunction representation that enables higher-order metaprogramming. More precisely, it's a class with a publicly-accessible nested Metafunction called apply. Correspondingly, a metafunction class invocation is defined as invocation of its nested apply metafunction.
In the following table and subsequent specifications, f is a Metafunction Class.
| Expression | Type | Complexity |
|---|---|---|
| f::apply::type | Any type | Unspecified. |
| f::apply<>::type | Any type | Unspecified. |
| f::apply<a1,...an>::type | Any type | Unspecified. |
typedef f::apply::type x;
| Precondition: | f is a nullary Metafunction Class; f::apply::type is a type-name. |
|---|---|
| Semantics: | x is the result of the metafunction class invocation. |
typedef f::apply<>::type x;
| Precondition: | f is a nullary Metafunction Class; f::apply<>::type is a type-name. |
|---|---|
| Semantics: | x is the result of the metafunction class invocation. |
typedef f::apply<a1,...an>::type x;
| Precondition: | f is an n-ary metafunction class; apply is a Metafunction. |
|---|---|
| Semantics: | x is the result of the metafunction class invocation with the actual arguments a1,... an. |