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

Unveiling the Nuances of reflect.ValueOf() and Value.Elem() in Go

In the realm of Go programming, the functions reflect.ValueOf() and the Value.Elem() method play distinct roles in exploring the intricacies of reflection. Let's delve into their differences and their applications.

The Essence of reflect.ValueOf()

reflect.ValueOf() serves as a gateway to the reflective world in Go. It takes an ordinary value, such as an integer or a string, and returns a Value descriptor that represents that value. This descriptor provides a handle to inspect and manipulate the underlying value in a structured manner.

The Purpose of Value.Elem()

Value.Elem() is a method exclusively available to reflect.Value instances. It retrieves the value embedded within an interface or the value pointed by a pointer. By stripping away the intermediary layer, it gives access to the concrete, underlying value.

Illustration

Consider the following code snippet:

var i int = 3
var p *int = &i

If we apply reflect.ValueOf() to this pointer:

v := reflect.ValueOf(p)

We retrieve a reflect.Value descriptor that represents the pointer itself (v). To access the value the pointer points to (3), we call v.Elem():

v2 := v.Elem()

Finally, to convert this reflect.Value back to a regular value, we use Interface():

value := v2.Interface().(int) // Type assertion required

Another Facet of Value.Elem()

Beyond unmasking values behind pointers and interfaces, Value.Elem() has an additional, less common use case. When passed a pointer to an interface, it retrieves the interface value wrapped under the interface pointer. Subsequent calls to Value.Elem() will unveil the concrete value stored within that interface.

Key Takeaway: When to Use Each Function

As a rule of thumb:

• Use reflect.ValueOf() to create a Value descriptor from a non-reflective value.
• Use Value.Elem() to peel away layers of indirection or interfaces to reach the underlying value.

Resources for Further Exploration

• The Go Blog: The Laws of Reflection: https://blog.golang.org/laws-of-reflection
• Go Data Structures: Interfaces: https://go.dev/blog/interfaces

The above is the detailed content of What's the Difference Between Go's `reflect.ValueOf()` and `Value.Elem()`?. For more information, please follow other related articles on the PHP Chinese website!