The empty interface (interface{} or any) is useful because it allows handling values of any type, making it ideal for generic operations, heterogeneous data storage, and dynamic data processing; 1. It enables functions to accept any type, such as printValue(x any) printing values of varying types; 2. It supports slices or maps with mixed types, like []any{42, "hello", 3.14}; 3. Type assertions or type switches extract the underlying type when needed; 4. The alias any (Go 1.18 ) is preferred over interface{} for clarity; 5. Use it for JSON, logs, and dynamic data, but avoid it in favor of generics when possible for better type safety and performance.
In Go, the empty interface—written as interface{} (prior to Go 1.18) or more cleanly as any (from Go 1.18 onward)—is an interface that has zero methods. Because it defines no requirements, every type in Go satisfies the empty interface.
This makes the empty interface a powerful tool for writing generic or flexible code when you don't know ahead of time what type you'll be working with.
Why is it useful?
Since any type implements the empty interface (by default), you can store any value in a variable of type interface{} or any. This is especially useful for:
- Functions that accept values of any type
- Storing heterogeneous data (like in a slice or map)
- Building generic utilities before Go had proper generics
? Note: With Go 1.18 , proper generics are available, so
anyis less often the best choice for truly generic logic. But it's still widely used in APIs, reflection, and when working with JSON, logs, etc.
Example: Using interface{} / any
package main
import "fmt"
func printValue(x interface{}) {
fmt.Printf("Value: %v, Type: %T\n", x, x)
}
func main() {
printValue(42) // int
printValue("hello") // string
printValue(3.14) // float64
printValue(true) // bool
}Output:
Value: 42, Type: int Value: hello, Type: string Value: 3.14, Type: float64 Value: true, Type: bool
Here, printValue accepts any type because interface{} can hold anything.
Common use case: Slices or maps with mixed types
data := []interface{}{
42,
"hello",
3.14,
true,
map[string]int{"age": 25},
}
for _, v := range data {
fmt.Printf("Type: %T, Value: %v\n", v, v)
}This creates a slice that can hold different types. Useful for parsing JSON or dynamic data.
Type assertions: Getting the original type back
Since interface{} hides the underlying type, you often need to extract the real type using a type assertion:
func process(x interface{}) {
if str, ok := x.(string); ok {
fmt.Println("It's a string:", str)
} else if num, ok := x.(int); ok {
fmt.Println("It's an int:", num)
} else {
fmt.Println("Unknown type")
}
}Or with a switch (type switch):
func process(x interface{}) {
switch v := x.(type) {
case string:
fmt.Println("String:", v)
case int:
fmt.Println("Int:", v)
case bool:
fmt.Println("Bool:", v)
default:
fmt.Printf("Unknown type: %T\n", v)
}
}any vs interface{}
As of Go 1.18, any is an alias for interface{}:
type any = interface{}So this is equivalent:
func printValue(x any) {
fmt.Printf("Value: %v, Type: %T\n", x, x)
}Using any is now preferred—it’s shorter and clearer.
When to use it (and when not to)
? Good use cases:
- Working with JSON (
map[string]interface{}) - Logging functions that take arbitrary data
- Interfacing with external data formats
- Legacy code or APIs expecting dynamic values
? Avoid when:
- You can use generics instead (cleaner, type-safe)
- Performance matters (interface{} has boxing/unboxing cost)
- You’re building reusable libraries—prefer explicit types or generics
Basically, the empty interface is Go’s way of saying “I don’t care what type this is.” It’s flexible but should be used carefully to avoid losing Go’s type safety benefits.
The above is the detailed content of what is the empty interface in go by example. For more information, please follow other related articles on the PHP Chinese website!
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