Sure, same as any other language with duck typing. Consider Ruby, which is famous for its duck typing. `variable.not_a_method` raises NoMethodError. How do you think it knows to do that? That's right, it first performs a type check and, since that check fails, it doesn't try to call the method and instead raises the exception. Exactly the same as Go panicking under the same circumstances.

> and then to something with a specific interface.

That is a type assertion, not a cast (Go doesn't have support for casts anyway). It merely asks the runtime: "Does this value satisfy the given type?" There is no change in type.

Now, let's take this further: It is generally agreed upon that duck typing differs from structural typing only in that it is evaluated dynamically instead of statically. Go's interface is quite clearly a structural type when evaluated statically.

And what do you think the type assertion does in the example given? That's right: It performs a type assertion on a "structural type" at run time. Duck typing, by definition!

> I don;t consider C a duck typing language too, because you can write ((Bird) ptr)->swim(), but perhaps you do?*

No. First and foremost, where would the typing come into play? That will actually try to call the method, whether the pointed memory is suitable or not. There is no type checking to steer you around mistakenly calling something that shouldn't be called. Not at compile time, not at run time.

It is literally called duck typing, not duck valuing. "Type" has significance. Where do you find it here?