有没有办法在链式调用中传播变量的“零”？

Question

I have the following in Go:

checkItemState := action.Data.CheckItem.State
if checkItemState != "" {
            fmt.Printf("checklist item state: %s", action.Data.CheckItem.State)
}

Now if any of the items in the chain action.Data.CheckItem are nil/empty, I get a nil pointer dereference error, which makes sense.

But is there a language level way to get checkItemState if not nil, or "" if any of the items in the chain are nil/empty.

(I come from Obj-C/Swift land where the nilness propagates)

Answer 1

You can handle this nicely if you code some getters. Go method receivers are just regular function arguments, so it's totally ok to call something on a nil receiver:

type Foo struct {
    Name string
}

func (f *Foo) GetName() string {
    if f == nil {
        return "default name" // or "", whatever
    }
    return f.Name
}

https://play.golang.org/p/Q20lSo65Kx

This trick is used e.g. by Go protobuf implementation.