Why Do Go Methods with Pointer Receivers Seem to Modify Value Arguments?

Why Does a Method with a Pointer Receiver Seem to Work with Value Arguments?

In Go's Tour of Go Exercise 51, the Scale method is described as having no effect on a Vertex value. However, experimentation reveals that Scale does modify the input value, even when passed a Vertex value instead of a pointer.

The Explanation

Go's strong typing requires that a method with a pointer receiver must be passed a pointer argument. However, the compiler intervenes under certain conditions and performs an implicit conversion, transforming the value argument into a pointer.

The "Magic" of the Compiler

When the method call x.m() is made, the compiler checks the following:

• The method set of the variable x's type includes m.
• The argument list provided can be assigned to the parameter list of m.

If these conditions are met and x is addressable (not copied), the compiler rewrites the code as (&x).m(). This conversion allows methods with pointer receivers to work with both pointers and values.

Significance

This implicit conversion is a key feature of Go's method sets. It enables methods to operate on pointers or values without requiring the programmer to explicitly manage pointers, simplifying code and improving readability.

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