Can Template Class Member Functions be Partially Specialized?

Partial Specialization of Template Class Members

Is it possible to specialize specific members of a template class? For example:

<code class="cpp">template <typename T, bool B>
struct X
{
    void Specialized();
};

template <typename T>
void X<T, true>::Specialized()
{
    // ...
}

template <typename T>
void X<T, false>::Specialized()
{
    // ...
}</code>

Answer:

Direct partial specialization of member functions within a class template is not allowed. However, full specializations can be provided:

<code class="cpp">template <>
void X<int, true>::Specialized()
{
    // ...
}</code>

Workarounds:

1. Overloaded Functions:

By introducing member function overloads, you can achieve a similar effect while retaining access to class members:

<code class="cpp">template <typename T, bool B>
struct X
{
    void Specialized() { SpecializedImpl(i2t<B>()); }

private:
    void SpecializedImpl(i2t<true>) { 
      // ...
    }

    void SpecializedImpl(i2t<false>) { 
      // ...
    }
};</code>

2. Deferring to Class Template:

Another option is to define a separate class template for specialized implementations:

<code class="cpp">template <typename T, bool B>
void X::Specialized() { SpecializedImpl<T, B>::call(); }</code>

3. SpecializedImpl for Function Overloading:

This approach emulates the i2t approach but allows for arbitrary parameter specialization:

<code class="cpp">template <typename T, bool B>
struct X
{
    void Specialized() { Specialized(SpecializedImpl<T, B>()); }

private:
    template <typename U>
    void Specialized(SpecializedImpl<U, true>) { // ... }

    template <typename U>
    void Specialized(SpecializedImpl<U, false>) { // ... }
};</code>

Conclusion:

While direct partial specialization of member functions is not possible, these workarounds provide effective alternatives for achieving similar functionality. The choice of approach depends on the specific requirements and preferences of the developer.

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