How Can I Prevent Implicit Conversions in Non-Constructing C Functions?

Avoiding Implicit Conversions in Non-Constructing Functions

Problem Formulation:

In C , non-constructing functions can implicitly cast parameters to match their declared types. This behavior, while convenient in some cases, can lead to unexpected results or compilation errors when attempting to restrict function parameters to specific types.

Solution:

To prevent implicit conversions and ensure that a non-constructing function only accepts parameters of a specific type, the following techniques can be employed:

1. Function Overloading with Template Deletions (C 11 and Later):

Define a function overload with a specific template type that matches the desired argument type. Then, declare another function template that is deleted for all other types. This effectively disables implicit conversions for that function:

void function(int);

// Delete overload for all other types
template<class T>
void function(T) = delete;

2. Class-based Function Overload Deletion (Pre-C 11):

An older approach for preventing implicit conversions involved creating a class with a private constructor that takes void pointers. Instantiating this class with the appropriate template arguments will delete all non-matching overloads:

class DeleteOverload
{
private:
    DeleteOverload(void*);
};

template<class T>
void function(T a, DeleteOverload = 0);

void function(int a)
{}

3. Static Assertions (C 23 and Later):

C 23 introduces the ability to use static assertions to verify that a function is called with the correct type. This approach provides a more explicit and informative error message compared to the previous methods:

void function(int) {}

template<class T>
void function(T) {
    // Static assertion fails when called with non-matching types
    static_assert(false, "function shall be called for int only");
}

By utilizing any of these techniques, it is possible to restrict a non-constructing function to accept parameters of a specific type and prevent implicit conversions from occurring.

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