Dune Core Modules (2.4.2)

Dune::AlwaysFalse< T > Struct Template Reference

template which always yields a false value More...

#include <dune/common/typetraits.hh>

Static Public Attributes

static const bool value = false
 always a false value
 

Detailed Description

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

template which always yields a false value

Template Parameters
TSome type. It sould 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,
"Instanciating this non-specialized template is an "
"error. You should use one of the specializations "
"instead.");
typedef void FrobnicateType;
};

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,
"Instanciating this non-specialized template is an "
"error. You should use one of the specializations "
"instead.");
typedef void FrobnicateType;
};
static const bool value
always a false value
Definition: typetraits.hh:392

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:
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