proposal: errors: add AsTarget(error)

[mkielar]

Proposal Details

Proposal details

Add following function to errors package:

func AsTarget[T error](err T) **T {
	p1 := &err
	p2 := &p1
	return p2
}

Rationale

Currently, when using errors.As, one has to do some acrobatics to create a double pointer to the type of error they want to test. This usually leads to following constructs:

type MyErr struct{}
func (e *MyError) Error() string {return "foo"}

... 
var myErr *MyErr // this is bloat
if errors.As(err, &myErr) {
    ...
}

Everytime one wants to use errors.As they have to first define a variable, and then use that variable. With AsTarget in place, this would be a bit simpler:

...
if errors.As(err, AsTarget(MyErr)) {
    ...
}

I'm very new to go, and I don't really understand the reasons why errors.As couldn't just accept a zero-instance of a type. But since it is what it is, would you consider adding AsTarget to the standard library?

[seankhliao]

Duplicate of #51945