Interface types and method sets

Canonical guidance

• a type implements an interface implicitly when its method set matches
• T and *T do not have the same method set
• interface values carry a dynamic type and value pair

Use when

• diagnosing assignability failures
• reviewing pointer versus value receivers
• explaining why an interface call compiles or not

Avoid

• assuming “has the method somewhere” is enough
• forgetting that only *T has methods with pointer receivers
• treating interface satisfaction as nominal inheritance

Preferred pattern

type Reader interface {
	Read([]byte) (int, error)
}

Anti-pattern

• assigning a T value to an interface that requires a method defined only on *T

Explanation: This is tempting because method-call syntax may auto-address some values, but interface satisfaction uses method sets, not call-site convenience.

Why

• method-set confusion is one of the highest-value retrieval gaps for code review and compile-error diagnosis