Can C Constructor Templates Exist Without Real Parameters?

Can Constructor Templates Exist Without Parameters?

In the realm of C programming, it is feasible to create non-template classes with template constructors lacking arguments. However, a potential conflict with the default constructor might arise.

Addressing the Potential Conflict

A straightforward workaround involves defining a template constructor within the non-template class, as showcased below:

class A {
  template<typename U>
  A(U* dummy) {
    // Custom operations here
  }
};

Delving into the Workaround

This approach circumvents the conflict with the default constructor by introducing a dummy argument (dummy). Despite its presence, this argument serves solely as a placeholder and does not actually affect the constructor's functionality. Its purpose is to facilitate argument deduction, allowing the compiler to infer the template parameters.

Exploring the Reasoning

Explicitly specifying template arguments when invoking a constructor template is not possible. Argument deduction is crucial for determining these arguments. Hence, the syntax:

Foo<int> f = Foo<int>();

Designates the as the template argument list for the Foo type, not its constructor. There is no designated place for the constructor template's argument list.

Examining the Workaround's Efficacy

Even with the devised workaround, inputting an argument remains necessary to invoke the constructor template. The ultimate objective of this approach is not entirely apparent.

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