Go | Receiver types, pointers, pass by value

[atc0005]

The receiver is passed by value, including the pointer receiver: it is a copy, and changing its value doesn't change the initial pointer receiver on which the method is called.

See "Why are receivers pass by value in Go?".

Relevance:

Attempting to implement the flags.Value interface with a Set() method on a pointer that happens to be nil and attempting to assign a valid pointer to the method receiver in the Set() method (which isn't allowed).

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This is clearly forbidden by the language spec. Spec: Method declarations:

The receiver is specified via an extra parameter section preceding the method name. That parameter section must declare a single non-variadic parameter, the receiver. Its type must be a defined type T or a pointer to a defined type T. T is called the receiver base type. A receiver base type cannot be a pointer or interface type and it must be defined in the same package as the method.

You can't declare a method with receiver type *T where T is already a pointer type, and you also cannot add methods for types defined in other packages. The type declaration and the method declaration must be in the same package.

Relevance:

Attempting to use a pointer to a type as the base which is already a pointer.

Refs:

• https://stackoverflow.com/questions/65440847/invalid-receiver-for-pointer-alias-type
• https://stackoverflow.com/questions/25520485/initialize-a-nil-pointer-struct-in-method