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Dune::AlwaysFalse< T > Struct Template Reference
Common » Utilities » C++ utilities and backports

template which always yields a false value More...

`#include <dune/common/typetraits.hh>`

Inheritance diagram for Dune::AlwaysFalse< T >:

## Detailed Description

template<typename T>
struct Dune::AlwaysFalse< T >

template which always yields a false value

Template Parameters

  T | Some type. It should be a type expression involving template parameters of the class or function using AlwaysFalse.

Suppose you have a template class. You want to document the required members of this class in the non-specialized template, but you know that actually instantiating the non-specialized template is an error. You can try something like this:

template<typename T>
struct Traits {
static_assert(false,
"Instantiating this non-specialized template is an "
"error. You should use one of the specializations "
"instead.");
The type used to frobnicate T
typedef void FrobnicateType;
};
Dune::type

This will trigger static_assert() as soon as the compiler reads the definition for the Traits template, since it knows that "false" can never become true, no matter what the template parameters of Traits are. As a workaround you can use AlwaysFalse: replace false by AlwaysFalse<T>::value, like this:

template<typename T>
struct Traits {
static_assert(AlwaysFalse<T>::value,
"Instantiating this non-specialized template is an "
"error. You should use one of the specializations "
"instead.");
The type used to frobnicate T
typedef void FrobnicateType;
};
Dune::AlwaysFalse
template which always yields a false value
Definition typetraits.hh:124

Since there might be an specialization of AlwaysFalse for template parameter T, the compiler cannot trigger static_assert() until the type of T is known, that is, until Traits<T> is instantiated.

The documentation for this struct was generated from the following file:

- typetraits.hh