How Can I Check if a Go Value Implements a Specific Interface at Compile Time or Runtime?

Checking if a Value Implements an Interface in Go

Validating whether a value conforms to a specified interface is a crucial aspect of Go programming. This question arises when the value's type is unknown, necessitating a dynamic check.

Dynamic Check with Type Assertions

In the code snippet provided, the val variable is an instance of MyType string, which does not directly implement the Somether interface. To dynamically check the type, use a type assertion:

_, ok := val.(Somether)

This assertion attempts to convert the val value to the Somether interface. The ok variable indicates if the conversion was successful (true) or not (false). However, this approach requires the value to be an interface type, which may not always be the case.

Compile-Time Check with Embedded Types

A more explicit method is to embed the desired interface into the value's type:

var _ Somether = (*MyType)(nil)

This syntax assigns a nil pointer of the value type to an interface variable. If the value type implements the interface, the code will compile without errors. Otherwise, the compiler will throw an error.

For example, in this case:

func (mt MyType) Method() bool { return true }

The MyType type implements the Method of the Somether interface. Therefore, the following code will compile and do nothing:

var _ Somether = (*MyType)(nil)

Importance of Compile-Time Check

In general, it is preferable to use compile-time checks to ensure that values implement interfaces at compile time rather than relying on dynamic checks at runtime. Compile-time checks provide stronger type safety and can prevent unforeseen errors.

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