具有接口类型的通道和指向结构的指针作为具体类型

Question

I'm attempting to generalize some of my code and I thought I might be able to pull some common code together, but I'm hitting my head against a type-system problem.

Let's assume I have an interface like this:

type Hashable interface {
    GetHash() []byte
}

and I have a couple of concrete types like this:

type Transaction struct {
    Hash                 []byte    `protobuf:"bytes,1,opt,name=hash,proto3" json:"hash,omitempty"`
}

func (m *Transaction) GetHash() []byte {
    if m != nil {
        return m.Hash
    }
    return nil
}

Notice that these are generated by protoc, and I can probably not change them easily. While the type itself does not implement Hashable, the pointer to the struct should if I'm not mistaken.

The issue arises when I create a function that accepts a channel of type chan Hashable and try to pass in a chan *Transaction, like this:

func consume(c chan Hashable) {
    // Do something with the elements from c
}

func main() {
    var c2 chan *Transaction
    consume(c2)
}

(I created a small example to show this issue in the Playground)

I could of course create a new struct that repacks the fields that consume needs, but that seems like a much worse option.

Is there a clean solution for this?

Answer 1

The problem is: chan *Transaction is not an interface - it's a specific type. So it cannot implement interface or chan Hashable by it's nature. You need to use specific channel.

You can convert Transaction values to Hashable on the fly with a grouting like this:

func convertor(ct chan *Transaction) chan Hashable {
    ch := make(chan Hashable)
    go func() {
        for t := range(ct) {
            ch <- Hashable(t)
        }

    }()
    return ch
}

and call

consume(convertor(c2))

https://play.golang.org/p/pd2EfhCehYz