Why Does sync.WaitGroup Have an Empty Method Set, Yet Its Methods Appear Callable on Non-Pointer Values?

Method Set of sync.WaitGroup

When working with Golang's sync.WaitGroup, one may encounter the question of its method set.

The Solution

• Empty Method Set:
  The method set of sync.WaitGroup is technically empty. This means that its methods cannot be directly invoked on non-pointer values.
• Pointer Receivers:
  All methods of sync.WaitGroup have pointer receivers, effectively making them part of the method set of the pointer type, *sync.WaitGroup.

The Reason

• Automatic Dereferencing:
  Despite the pointer receiver requirement, calls to sync.WaitGroup methods on non-pointer values are possible due to automatic dereferencing.
• Shorthand Notation:
  In such cases, the compiler implicitly takes the address of the non-pointer value and uses it as the method receiver. This effectively translates wg.Add(1) to (&wg).Add(1).

Example

In the provided code snippet, wg is declared as a value of type sync.WaitGroup. The subsequent method calls (wg.Add, wg.Done, etc.) are allowed because the compiler automatically dereferences wg and treats it as a pointer.

Related Question

Refer to the following question for further understanding:

• Calling a method with a pointer receiver by an object instead of a pointer to it?

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