C++: how to choose the constructor depending on the condition?

Question

Assume I have a class with different constructors:

class A
{
public:
    A(char* string)
    {
        //...
    }

    A(int value)
    {
        //..
    }

           


        

Answer 1

A a = isTrue() ? A("string") : A(10);

And if a.check() is a const member function, an alternative may be better:

const A& a = isTrue() ? A("string") : A(10);

The object will be destroyed when the reference a go out of scope.

Note since C++17, according to the rule of copy elision the copy/move constructor is not required to be accessible for this case; copy elision is guaranteed here.

And since C++17 you can use std::optional, which doesn't cause any dynamic memory allocation. e.g.

std::optional a;
if (isTrue())
{
    a.emplace("string");
}
else
{
    a.emplace(10);
}
(*a).check();

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^{BTW: A(char* string) is supposed to be A(const char* string).}