How Can I Check if a Value Implements an Interface in Go?

Checking Interface Implementation in Go

In Go, using interfaces provides a way to define common behavior for different data types. However, determining if a value implements a specific interface can be tricky.

Type Assertion vs. Type Switch

The most common method for checking if a value implements an interface is through type assertion:

_, ok := val.(Somether)

This type assertion verifies if the value val can be converted to the type Somether. If it can, it assigns the converted value to _ and sets ok to true; otherwise, it sets ok to false.

However, type assertion assumes that val is an interface, which may not always be the case. For explicit type checking, you can use the type switch method:

var _ Somether = (*MyType)(nil)

In this example, we are declaring an unnamed variable of type Somether and setting it equal to a nil pointer of type MyType. This syntax ensures that the compiler verifies if MyType implements Somether, triggering a compile error if it does not.

Simplicity of Known Types

It's important to note that if the type of val is known, the compiler automatically checks if it implements Somether. The explicit checks described above are only necessary when the type is unknown.

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