I need some help understand the behaviour of my code[1].  Specifically I have trouble with `add` method on line 79.

My impression is that since it returns `this`, multiple invocations can be chained like `obj.add(X).add(Y).add(Z)`.  However the test on line 92 fails and if I do a `writeln`, only "p1" and "p2" records show up.

What am I missing here?  Thanks in advance.

[1] https://github.com/bahmanm/d-etudes/blob/master/source/e002/models.d

On Monday, 7 September 2015 at 14:12:25 UTC, Bahman Movaqar wrote:
> I need some help understand the behaviour of my code[1].  Specifically I have trouble with `add` method on line 79.
>
> My impression is that since it returns `this`, multiple invocations can be chained like `obj.add(X).add(Y).add(Z)`.  However the test on line 92 fails and if I do a `writeln`, only "p1" and "p2" records show up.
>
> What am I missing here?  Thanks in advance.
>
> [1] https://github.com/bahmanm/d-etudes/blob/master/source/e002/models.d

struct is a value type,you can convert to ref type by "ref":

    struct Test
    {
        int a;

        Test add1()
        {
            a++;
            return this;
        }
        ref Test add2()
        {
            a++;
            return this;
        }
    }

    Test t1;
    t1.add1.add1;
    writeln(t1.a);//1

    Test t2;
    t2.add2.add2;
    writeln(t2.a);//2

On Monday, 7 September 2015 at 14:12:25 UTC, Bahman Movaqar wrote:
> I need some help understand the behaviour of my code[1].  Specifically I have trouble with `add` method on line 79.
>
> My impression is that since it returns `this`, multiple invocations can be chained like `obj.add(X).add(Y).add(Z)`.  However the test on line 92 fails and if I do a `writeln`, only "p1" and "p2" records show up.
>
> What am I missing here?  Thanks in advance.
>
> [1] https://github.com/bahmanm/d-etudes/blob/master/source/e002/models.d

You should mark your return type with ref. Structs are value types and therefore you return only a copy currently.

On Monday, 7 September 2015 at 14:26:57 UTC, mzfhhhh wrote:
> On Monday, 7 September 2015 at 14:12:25 UTC, Bahman Movaqar wrote:
> struct is a value type,you can convert to ref type by "ref":
>
>     struct Test
>     {
>         int a;
>
>         Test add1()
>         {
>             a++;
>             return this;
>         }
>         ref Test add2()
>         {
>             a++;
>             return this;
>         }
>     }
>
>     Test t1;
>     t1.add1.add1;
>     writeln(t1.a);//1
>
>     Test t2;
>     t2.add2.add2;
>     writeln(t2.a);//2

Thanks.  I was afraid I had to resort to using pointers to achieve this!

On Monday, 7 September 2015 at 14:28:06 UTC, Namespace wrote:
> On Monday, 7 September 2015 at 14:12:25 UTC, Bahman Movaqar wrote:
> Structs are value types and therefore you return only a copy currently.

Does this mean that in the following piece of code, what is passed to `add` is actually a copy of `rec1`?

   auto rec1 = SalesRecord("p10", 1.0, 10);
   coll.add(rec1);

On 2015-09-07 16:44, Bahman Movaqar wrote:

> Does this mean that in the following piece of code, what is passed to
> `add` is actually a copy of `rec1`?
>
>     auto rec1 = SalesRecord("p10", 1.0, 10);
>     coll.add(rec1);

Yes. structs have value semantics. If you want reference semantics you might want to use a class instead.

-- 
/Jacob Carlborg

On Monday, 7 September 2015 at 14:54:04 UTC, Jacob Carlborg wrote:
> On 2015-09-07 16:44, Bahman Movaqar wrote:
>
>> Does this mean that in the following piece of code, what is passed to
>> `add` is actually a copy of `rec1`?
>>
>>     auto rec1 = SalesRecord("p10", 1.0, 10);
>>     coll.add(rec1);
>
> Yes. structs have value semantics. If you want reference semantics you might want to use a class instead.

Actually I like the value semantics very much.  I think I'm going to stick to `structs` for as much as possible :-)