Why Do Constructors Have No Return Value?

• #design

Just now, a classmate asked me a question: What does it mean to new a member function in C++?

…I thought to myself, a new member function? Is there such an operation?

Later I asked, is the name of this member function the same as the class name?

He said yes, it’s the constructor.

…Isn’t that just newing an object?

Then he asked a profound question: Why don’t constructors have return values?

I said that new is for the class, the part after new refers to the class name, not a member function.

But the class doesn’t have parameters?

The constructor has parameters.

But the constructor has no return value?

Huh?

Here is a simple piece of code:

#include <iostream>
using namespace std;

class Test
{
    public:
        Test(int num);
};

// Constructor, has parameters but no return value
Test::Test(int num)
{
    cout << num << endl;
}

int main()
{
    // Object assigned to a variable
    Test* test = new Test(1);
    return 0;
}

Actually, you can think of this scenario without looking at the code. When you new an object, is the variable after new referring to the class name or the method name?

If it refers to the class name, the class itself has no parameters, and no return value. Moreover, the behavior of the new keyword in the code would be different from other statements. Additionally, the class has a default no-argument constructor. If new is for the class, why do we need the default constructor?

If it refers to the function name, the constructor has no return value. As in the code above, it’s clear that new Test(1) is assigned to Test* test.

Why don’t constructors have return values? Because when a constructor executes, it tells the compiler how much space to allocate in memory, initializes member variables, determines the address of this, and after doing these things, it doesn’t allow the user to customize the return type? Because the return value of the constructor is always and must be itself, it’s not transparent to the user (why does the compiler “presumptuously” do this)?

Why don’t constructors have return values? I don’t know the answer to this question, nor am I very interested in knowing. But this question has given me great inspiration and a lot of shock. The phrase “new member function” is really a novel idea. We take too many things for granted, as a matter of course, thinking it should be that way, but rarely ask why it is that way, and rarely seriously think about and understand many things.