Constructor conversion
If you define a
constructor that takes as its single argument an object
(or reference) of another type, that constructor allows the compiler to perform
an automatic type conversion. For example,
//: C12:AutomaticTypeConversion.cpp
// Type conversion constructor
class One {
public:
One() {}
};
class Two {
public:
Two(const One&) {}
};
void f(Two) {}
int main() {
One one;
f(one); // Wants a Two, has a One
} ///:~
When the compiler sees f( )
called with a One object, it looks at the declaration for
f( ) and notices it wants a Two. Then it looks to see if
there’s any way to get a Two from a One, and it finds the
constructor Two::Two(One), which it quietly calls. The resulting
Two object is handed to f( ).
In this case, automatic type conversion
has saved you from the trouble of defining two overloaded versions of
f( ). However, the cost is the hidden constructor call to
Two, which may matter if you’re concerned about the efficiency of
calls to f( ).
