Error: xxx is not an lvalue

[Unknown W. Brackets]

Well, if you really want a "protected" associative array, or array for 
that matter, you probably should define a wrapper class that inlines the 
access you're willing to allow.

 From a basic perspective, _testMap is a structure of data.  Although it 
is private, there's no reason it can't be modified through an accessor.

Without a setter, the only thing that should fail is test.testMap = 
something.  Requiring a setter for any minor change makes no sense.

Compare it to this: if you have a class that has a member object (e.g. a 
User with a Socket member variable), should it be necessary to have a 
setter to change the Socket?  Can't the Socket handle its own 
private/public-ness?

Arrays and associative arrays are the same, except that the members you 
use are public.

-[Unknown]


Tyro[a.c.edwards] wrote:
> On 5/3/2009 6:25 PM, Unknown W. Brackets wrote:
>> This code works fine (D 2.x only):
>>
>> class Test
>> {
>> private int[int] _testMap;
>> public ref int[int] testMap() {return _testMap;}
>> }
>>
>> void main()
>> {
>> Test test = new Test();
>> test.testMap[0] = 1;
>> }
>>
>> Note the "ref". Otherwise, a value is returned which is not modifiable.
>> This will also fix test.array.length. Nothing wrong here, no creepy bad
>> temporary property problems.
> 
> Is this an intended or even desirable "feature" of the language or just 
> something that happens to work in D 2.x? I ask because to the untrained 
> eye, it is unclear exactly what is happening. There is nothing to inform 
> me that _testMap can be modified from outside the class. Even with "ref" 
> there it doesn't make it any clearer.
> 
> Matter of fact, I just had a problem in Phobos 2 where a function was 
> defined like that and I had to comment out the "ref" for it to work. 
> Kept telling me that some array was not an lvalue. The minute I 
> commented out the "ref", everything worked like a charm.
> 
> Also it makes more sense to me to have separate functions as getters and 
> setters. Maybe that's only because I lacking proper training in the art 
> of computer programming though.
> 
>> I suppose you could also try returning a pointer to an associative array
>> (e.g. with &) in D 1.x.
>>
>> -[Unknown]
>>
>> flourish wrote:
>>> Hi,
>>>
>>> why does the following code not compile -- or how to declare a (usable)
>>> property of an associative array field?
>>>
>>> //////////////////////
>>> class Test
>>> {
>>> private int[int] _testMap;
>>> public int[int] testMap() {return _testMap;}
>>> }
>>>
>>>
>>> void main()
>>> {
>>> Test test = new Test();
>>> test.testMap[0] = 1;
>>> }
>>> /////////////////
>>>
>>> *** Error: test.testMap() is not an lvalue
>>>
>>>
>>> Regards,
>>> flourish
>>>
>>>
>>>
>