Ensure a type implements an interface at compile time in Go

Assuming the question is about Go, e.g.

var _ foo.RequiredInterface = myType{} // or &myType{} or [&]myType if scalar

as a TLD will check that for you at compile time.

In the Go language there is no "implements" declaration by design. The only way to ask the compiler to check that the type T implements the interface I by attempting an assignment (yes, a dummy one). Note, Go lang differentiates methods declared on structure and pointer, use the right one in the assignment check!

type T struct{}
var _ I = T{}       // Verify that T implements I.
var _ I = (*T)(nil) // Verify that *T implements I.

Read FAQ for details Why doesn't Go have "implements" declarations?