On Mon, Apr 02, 2018 at 10:26:32AM +0000, RazvanN via Digitalmars-d-learn wrote:
> Hi all,
>
> Let's say we have this code:
>
> struct B
> {
> int a;
> this(int a) immutable
> {
> this.a = 7;
> }
>
> this(int a)
> {
> this.a = 10;
> }
> }
>
> void main()
> {
> B a = immutable B(2);
> writeln(a.a);
> a.a = 4;
>
> immutable B a2 = immutable B(3);
> writeln(a2.a);
> a2.a = 3; // error : cannot modify
> }
>
> Both a and a2 will be constructed using the immutable constructor,
> however a is not immutable (a.a = 4 will compile fine). Is this the
> intended behavior?
> Shouldn't the compiler warn me that I'm trying to create a mutable
> object using the constructor for an immutable object? I couldn't find
> any documentation about this.
What's happening here is that B is a value type, meaning that assignment
makes a copy of the object. Since B has no fields that contain
indirections, when a copy of B is made, it is completely independent of
the original immutable object, so it's perfectly fine to make the copy
mutable.
T
--
Meat: euphemism for dead animal. -- Flora
