what is the law of big two

Question

Hi

I have came across the rule of 0,3 or 5, but never heard about law of big two.

If I heard it correctly, it is same as rule of 3, but without the need to define own destructor. Is that correct? If so, where is memory allocated is released? If memory is not allocated dynamically , why one would opt for rule of 3 in first place?

Any example scenario or code for the law of big two would be helpful to understand.

Answer 1

You're right about the Law of the Big Two—it's closely related to the Rule of Three and the Rule of Five in C++. Here's a breakdown to clarify:

Law of the Big Two
The Law of the Big Two states that if you need to define either a custom copy constructor or a custom copy assignment operator, you should also define the other. In essence, you are dealing with resource management and need to ensure proper copying and assignment behavior.

Key Points:

The Law of the Big Two implies that if you need to customize either the copy constructor or the copy assignment operator, you should also provide a custom destructor.
It focuses on the need to manage resources (like dynamic memory) properly to avoid issues like double deletion or resource leaks.
Rule of Three vs. Law of the Big Two
Rule of Three: States that if you need to define a custom destructor, copy constructor, or copy assignment operator, you should define all three. This is to ensure that resource management is handled correctly.
Law of the Big Two: Refers to the fact that in many cases, you need to define just the destructor and either the copy constructor or copy assignment operator. This is because modern C++ often relies on move semantics, making the Rule of Five less frequently necessary.
Memory Management
If you use the Rule of Three or the Law of the Big Two, you are typically managing dynamic memory or other resources manually.

Where is memory allocated or released?

If you allocate memory dynamically using new, you need to release it using delete in the destructor.
If you do not use dynamic memory allocation, the need for a custom destructor might not arise, but you still need to manage the copying and assignment correctly.