Why do constructors not return values?

constructor
Dr. Rajesh Rolen picture Dr. Rajesh Rolen · Nov 24, 2009 · Viewed 86.1k times · Source

Please tell me why the constructor does not return any value. I want a perfect technical reason to explain to my students why the constructor does not have any return type.

Answer

Dathan picture Dathan · Nov 24, 2009

What actually happens with the constructor is that the runtime uses type data generated by the compiler to determine how much space is needed to store an object instance in memory, be it on the stack or on the heap.

This space includes all members variables and the vtbl. After this space is allocated, the constructor is called as an internal part of the instantiation and initialization process to initialize the contents of the fields.

Then, when the constructor exits, the runtime returns the newly-created instance. So the reason the constructor doesn't return a value is because it's not called directly by your code, it's called by the memory allocation and object initialization code in the runtime.

Its return value (if it actually has one when compiled down to machine code) is opaque to the user - therefore, you can't specify it.

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