Transfer ownership (Genie/Vala)

There is a simple example:

struct MyStruct
    a: int
    b: int

def my_proc(): unowned list of MyStruct
    var result = new list of MyStruct
    var my_struct = MyStruct()
    for var i = 1 to 10
        my_struct.a = i
        my_struct.b = i*i
        result.add(my_struct)
    return result

init
    pass

in case of compilation of this code, there is an error: "Local variable with strong reference used as return value and method return type has not been declared to transfer ownership". How to change a code that compilation took place successfully?

A Genie list is really a Gee.List<T> in "disguise" which is a class type, so it will be reference counted.

Also a type inferred var variable is currently always an owned variable (there is a bug report about this in the Vala bug tracker).

So result a strong reference to a class instance. You can't return that as an unowned reference.

I'd strongly advice you to use a class instead of a struct for MyStruct.

Otherwise you will have memory management problems (structs are not reference counted).

You don't have to worry about copying and ownership then:

class MyStruct
    a: int
    b: int

def my_proc(): list of MyStruct
    var result = new list of MyStruct
    for var i = 1 to 10
        var my_struct = new MyStruct()
        my_struct.a = i
        my_struct.b = i*i
        result.add(my_struct)
    return result

init
    pass

Edit: If you want the list to contain multiple values, you have to allocate my_struct inside the loop as well! I have updated my code to reflect that.