Boxing and Unboxing

Boxing is the process of converting a non-object primitive value into an object. It is as easy as it sounds. You create a wrapper class which you instantiate and initialize with the non-object value:

Unboxing is the reverse of boxing: You downgrade a full object to a mere scalar value by retrieving the boxed value from the box object.

It is important to notice that changes to the boxed value does not affect the original value and vice verse. The code below illustrates both steps:

@Boxee = global i32 17

%Integer = type { i32 }

define void @Integer_Create(%Integer* %this, i32 %value) nounwind {
    ; you might set up a vtable and associated virtual methods here
    %1 = getelementptr %Integer, %Integer* %this, i32 0, i32 0
    store i32 %value, i32* %1
    ret void
}

define i32 @Integer_GetValue(%Integer* %this) nounwind {
    %1 = getelementptr %Integer, %Integer* %this, i32 0, i32 0
    %2 = load i32, i32* %1
    ret i32 %2
}

define i32 @main() nounwind {
    ; box @Boxee in an instance of %Integer
    %1 = load i32, i32* @Boxee
    %2 = alloca %Integer
    call void @Integer_Create(%Integer* %2, i32 %1)

    ; unbox @Boxee from an instance of %Integer
    %3 = call i32 @Integer_GetValue(%Integer* %2)

    ret i32 0
}