Interface satisfaction is implicit in Go

Developers expect to declare 'implements' like in Java/C#. In Go, types satisfy interfaces implicitly, which can lead to silent failures when method signatures drift.

Use a compile-time assertion to verify interface satisfaction:

type Storer interface {
    Save(ctx context.Context, item Item) error
    Load(ctx context.Context, id string) (Item, error)
}

type PostgresStore struct{}

// Compile-time check — fails to compile if PostgresStore doesn't satisfy Storer
var _ Storer = (*PostgresStore)(nil)

func (s *PostgresStore) Save(ctx context.Context, item Item) error { ... }
func (s *PostgresStore) Load(ctx context.Context, id string) (Item, error) { ... }

The blank identifier assignment forces the compiler to check assignability without allocating.

Go's structural typing means any type with the right method set satisfies an interface. The compiler only checks this at the point of assignment, not at type declaration. Explicit assertions catch drift early.