Nice, congratulations on the release.
I'd really like to see some progress on generics / parametric types. I'm starting to get the impression that it will never happen.
I'd really like to see some progress on generics / parametric types. I'm starting to get the impression that it will never happen.
From the FAQ: "Generics are convenient but they come at a cost in complexity in the type system and run-time. We haven't yet found a design that gives value proportionate to the complexity, although we continue to think about it. Meanwhile, Go's built-in maps and slices, plus the ability to use the empty interface to construct containers (with explicit unboxing) mean in many cases it is possible to write code that does what generics would enable, if less smoothly.
This remains an open issue."
The other constant line from the Go implementers is something like "generics have proven troublesome in [unnamed] other languages, so we don't want them until we're sure we can get them right". This may be a reference to C++, in which compiling templates turns out to be a real pain. But at this point, the literature is full of better ways to do it.
I'm not versed in Go, but does that mean something similar to (Java-style) Object[] and explicit casting of each value you get out of the list?
http://play.golang.org/p/L5hprjhqN_
In this example, one function probes the underlying type by using t.(type), and the other one uses a type assertion by doing a val, ok := t.(int) - The type assertion will return the value of the integer and true if t happens to be an integer (a Go function can return multiple values)
If you pass an object as an "empty interface{}" you can test the underlying type.
edit: Note that you can only use a type assertion with an interface! So, this fails: http://play.golang.org/p/0BtSWfE3f2 but this doesn't: http://play.golang.org/p/tZB4Jivp3z
So, the answer is that it is pretty much the same as in Java, since there you also use reflection to get the type of Object:
if (o instanceof String) {...}
The difference is that Java stores the type in the actual instance, while Go stores the type in the 'reference' (which is normally a type-pointer tuple). Unfortunately, Go's approach can lead to the situation where nil (null) is not nil, when two references have null as its pointer, but different types.
Interfaces in a nutshell:
Go checks at compile-time that any concrete variable passed where in interface is expected satisfies the methods of that interface.
Conversely, Go checks at compile-time that the program never attempts to invoke methods on an interface value that are not guaranteed by the interface.
In this example, there is a compile-time error (not a runtime error), because we attempt to call a non-guaranteed method on an interface value, even though the underlying value satisfies this interface: http://play.golang.org/p/EaQQpv-NAW
This provides type safety: if your program compiles, you know that you will never run into a runtime error by trying to invoke an undefined method.
When you do type assertions, you're using reflection (ie, http://golang.org/pkg/reflect/) to determine the underlying value at runtime.
However, remember that using type assertions essentially sidesteps the benefits of having interfaces. Interfaces allow you to invoke function calls with type safety on values of unknown type, as long as it is known that the underlying type provides the required set of methods.