Given any function that takes a parameter of type interface{} how would I know whether or not to pass that parameter with or without & without navigating the source code of the function.
For example if I had a function with this type signature given to me:
func foo(x interface{}, y int) int
Would there be any way to figure out if x was supposed to be passed by value or by pointer?
分享 Here is the snippet from the source:
// DecodeElement works like Unmarshal except that it takes
// a pointer to the start XML element to decode into v.
// It is useful when a client reads some raw XML tokens itself
// but also wants to defer to Unmarshal for some elements.
func (d *Decoder) DecodeElement(v interface{}, start *StartElement) error {
val := reflect.ValueOf(v)
if val.Kind() != reflect.Ptr {
return errors.New("non-pointer passed to Unmarshal")
}
return d.unmarshal(val.Elem(), start)
}
It is checking val.Kind() != reflect.Ptr Which means you have to pass the pointer i.e &v.
Its entirely depend on the person who wrote the method or function, so interface{} could be either *ptr or anything but u ve to check that inside your function using reflect.ValueOf(v).Kind() whether the value is a pointer or not and proceeds accordingly.
And little bit about empty interface:
The interface type that specifies zero methods is known as the empty interface:
interface{}
An empty interface may hold values of any type. (Every type implements at least zero methods.)
Empty interfaces are used by code that handles values of unknown type. For example, fmt.Print takes any number of arguments of type interface{}.
Another useful discussion: docs
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