Can You Force Initialization of Static Members in Template Classes Without Instantiation?

How to Explicitly Initialize Static Members

Question:

In C , static members of a template class are only initialized when explicitly used within a concrete instantiation. Is there a way to force their initialization without creating an instance or requiring the user to specify the member directly?

Answer:

Yes, it is possible to force the initialization of a static member by employing one of the following techniques:

Using a Wrapper Type:

<code class="cpp">template<typename T, T> struct value { };

template<typename T>
struct HasStatics {
  static int a; // we force this to be initialized
  typedef value<int&amp;, a> value_user;
};

template<typename T>
int HasStatics<T>::a = /* whatever side-effect you want */ 0;</code>

Using a Syntactic Trick:

<code class="cpp">template<typename T, T> struct var { enum { value }; };
typedef char user;

template<typename T>
struct HasStatics {
  static int a; // we force this to be initialized
  static int b; // and this

  // hope you like the syntax!
  user :var<int&amp;, a>::value,
       :var<int&amp;, b>::value;
};

template<typename T>
int HasStatics<T>::a = /* whatever side-effect you want */ 0;

template<typename T>
int HasStatics<T>::b = /* whatever side-effect you want */ 0;</code>

Both techniques force the initialization of the static members by introducing a dependency that triggers the evaluation of the member's definition. Note that the second technique involves unconventional syntax and may not be suitable for all cases.

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