Why Go Interfaces Are Implicitly Satisfied (No implements Keyword)

Go interfaces are implicitly satisfied because the compiler checks if a type has all the methods defined in the interface at compile time, rather than requiring an explicit declaration. If a type implements the required methods, it automatically satisfies the interface without any extra syntax.

type Reader struct{}

// No 'implements io.Reader' keyword needed.
// Satisfies interface because Read method exists.
func (r *Reader) Read(p []byte) (n int, err error) {
    return 0, nil
}

// Usage: The compiler verifies satisfaction here.
var _ io.Reader = &Reader{}

Implicit satisfaction means a type automatically becomes compatible with an interface simply by having the right methods, without needing to declare it. This works like a key fitting a lock: if the key has the correct shape (methods), it fits the lock (interface) regardless of whether you labeled it as such. It reduces boilerplate code and allows types to satisfy multiple interfaces naturally.