Define function with parameter whose type has an embedded type in Go

Question

Very new to Go and so probably going about this the wrong way.

Let's say I have a type:

type Message struct {
    MessageID string
    typeID    string
}

And I create another type with Message embedded:

type TextMessage struct {
    Message
    Text       string
}

And then I want to create a function that will take any type, so long as it has Message embedded:

func sendMessage(???===>msg Message<===???) error

How do I do that? My goal is to define the function such that it requires a type with a typeID member/field. It would be ok (but less desirable) if it took an interface, in which case I assume I'd just define the interface and then define the appropriate method. But unless that's the only way to accomplish this - what's the recommended approach?

Interface - definitely. Your other option is to accept an interface and type assert it in the function .. but thats icky-pants when there's a more type-safe way. — Simon Whitehead
– Simon Whitehead, Commented Nov 5, 2014 at 0:06
Ok, that's not so bad after I try it out. Wanted to make sure I wasn't missing some obvious modality. Make it an answer so I can accept? — Michael
– Michael, Commented Nov 5, 2014 at 0:46
@4of4: You don't need to change every single instance of Golang to go. It's not important, and both are acceptable names (as seen in the tag wiki excerpt). — Pokechu22
– Pokechu22, Commented Nov 8, 2014 at 0:13

Simon Whitehead · Accepted Answer · 2014-11-05 00:52:28Z

1

I would go the interface route:

type TypeIdentifier interface {
    TypeId() string
}

func sendMessage(t TypeIdentifier) {
    id := t.TypeId()
    // etc..
}

Your only other option is to type assert an interface{} within the function.. which will quickly become an out-of-control bowl of bolognese.

answered Nov 5, 2014 at 0:52

Simon Whitehead

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2 Comments

Michael Over a year ago

At first, the function seemed like overkill. But once I got past that it flows nicely and allows the typeID to stay out sight, like I'd prefer.

Simon Whitehead Over a year ago

More and more I find myself defining interfaces for this purpose and the code - although more of it - becomes much more finely tuned and clean. Everything just has small specific purposes and it flows nicely.

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