How to Resolve the \'Interface Method Must Have No Type Parameters\' Error in Go Generics?

How to Overcome "Interface Method Must Have No Type Parameters" Error in Go Generics?

When implementing generics in Go, you may encounter the error "interface method must have no type parameters." This error arises because, by design, type parameters are not permitted in interface methods. This design decision was made to prevent ambiguity and performance implications arising from multiple interpretations of methods with type parameters in interface definitions.

To address this issue, you can relocate the type parameter into the interface type definition. Consider this modified code:

type Reader[V Unmarshaler] interface {
    Read(bucket []byte, k ...[]byte) ([][]byte, error)
    ReadDoc(bucket []byte, factory func() (V, error), k ...[]byte) ([]V, error)
}

type Unmarshaler interface {
    UnmarshalKV(v []byte) error
}

In this modified code, the type parameter V is moved from the method signature to the interface type definition itself. This effectively parameterizes the interface with the type V, allowing you to specify the concrete type when implementing the interface.

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