What's the Difference Between `reflect.ValueOf()` and `Value.Elem()` in Go?

Understanding the Difference Between reflect.ValueOf() and Value.Elem()

Reflect.ValueOf() serves as the gateway to reflection, allowing you to obtain a reflect.Value descriptor for non-reflection values like strings or integers.

On the other hand, Value.Elem() functions as a method within reflect.Value. It can be employed to retrieve the value (also a reflect.Value) referenced by the value encapsulated by the original reflect.Value. Note that reflect.Indirect() can also be utilized for this purpose.

To transition from reflection back to non-reflection, use the Value.Interface() method, which returns the wrapped value as a simple interface{}.

var i int = 3
var p *int = &i
fmt.Println(p, i) // Output: 0x414020 3

v := reflect.ValueOf(p)
fmt.Println(v.Interface()) // Output: 0x414020

v2 := v.Elem()
fmt.Println(v2.Interface()) // Output: 3

Advanced Use Case: Value.Elem() for Interfaces

If reflect.Value wraps an interface value, Value.Elem() can also retrieve the concrete value within that interface.

var r io.Reader = os.Stdin

v := reflect.ValueOf(r)
fmt.Println(v.Type()) // Output: *os.File

v2 := reflect.ValueOf(&r)
fmt.Println(v2.Type()) // Output: *io.Reader
fmt.Println(v2.Elem().Type()) // Output: io.Reader
fmt.Println(v2.Elem().Elem().Type()) // Output: *os.File

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