proposal: Make nil nil again

[okm-8]

Proposal Details

Due to learn the issue #70364 I would like to make a proposal:

way one: Because nil is suitable value for any interface, it should be possible to check a value is nll despite some function return nil as a pointer to the concrete type that implements this interface

OR

way two: nil should not to be suitable as value for any interface (As it usually working)

I, personally, mean that it is not correct way to mess pointer and reference, so passing nil as a reference should be prohibited

package main

import (
	"fmt"
)

type Unwrapable interface {
	Unwrap() error
}

type TestStruct struct {
	err error
}

func (err *TestStruct) Unwrap() error {
	return err.err
}

func doSomethingElse() *TestStruct {
	return nil
}

func HandleUnwrapable(err Unwrapable) {
        // should be possible ever by the way one
	if err != nil {
		fmt.Printf("err: Not nil, type: %T, address: %p\n", err, err)
	} else {
		fmt.Printf("err: Nil, type: %T, address: %p\n", err, err)
	}
}

func main() {
	test := doSomethingElse()

	if test != nil {
		fmt.Printf("err: Not nil, type: %T, address: %p\n", test, test)
	} else {
		fmt.Printf("err: Nil, type: %T, address: %p\n", test, test)
	}

	HandleUnwrapable(test) // should be prohibited by the way two

	// Output
	// err: Nil, type: *main.TestStruct, address: 0x0
        // err: Not nil, type: *main.TestStruct, address: 0x0 - unexpected
}

Others languages behaviour with nil reference

[gabyhelp]

Related Issues

• proposal: Go 2: add built-in null for zero value of pointers #61489 (closed)
• proposal: errors: Is resolve nil error problem #40674 (closed)
• proposal: Go 2: require explicit type cast to create "nil receiver" interface #30294 (closed)
• Simplify if condition for nil checking #68127 (closed)
• proposal: Go 2: use an identifier other than nil for uninitialized interfaces #24682 (closed)
• go compiler to raise an error if function not explicitly `return nil` with return value of interface type signature #46627 (closed)
• proposal: Go 2: Ban typed nil interfaces through banning nil method receivers #27890 (closed)
• proposal: Go 2: equality between an interface and nil should by default compare only by value (and not also type) #60786 (closed)
• proposal: Go 2: explicit nil and pointer param #36884 (closed)

Related Discussions

• nil interfaces: a proposal

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

see the above links

[Jorropo]

This has been already discussed before and you need a story on how to do without introducing a backward breaking change to the language for a proposal like this to be considerable.

Also https://go.dev/doc/faq#nil_error