::value^::type #typedef

This TMP technique is the simplest but not for the uninitiated.

In type_traits.h, many templates expose a ::value or ::type construct. Often these two “members” are the only visible output from the type trait meta-functions.

  • ::value is a static field, typically true/false
  • ::type is a member typedef, typically related to the type argument T, but can be “void” like in enable_if

 

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