Interface Satisfaction

• A type satisfies an interface if it implements all the methods the interface requires.
• *os.File
  • *os.File satisfies io.Reader, Writer, Closer, and ReadWriter.
• *bytes.Buffer
  • A bytes.Buffer satisfies io.Reader, Writer, and ReadWriter.
  • Does not satisfy Closer as it does not have a Close method.

Assignability(分配) Rule

• An expression may be assigned to an interface only if its type satisfies the interface.

Concealing(隱瞞) the concrete type and value

• Interface wraps concrete type, only methods defined by interface are revealed even if concrete type implements others.