Neat trick - 'with' and unnamed objects + 'with' proposals

[Max Samukha]

On Wed, 25 Apr 2007 02:35:02 +0900, Bill Baxter
<dnewsgroup at billbaxter.com> wrote:

>Max Samukha wrote:
>> On Wed, 25 Apr 2007 01:53:56 +0900, Bill Baxter
>> <dnewsgroup at billbaxter.com> wrote:
>> 
>>> BCS wrote:
>>>> Bill Baxter wrote:
>>>>> BCS wrote:
>>>>>
>>>>>> Bill Baxter wrote:
>>>>>
>>>>>> how about take a trick from "if"
>>>>>>
>>>>>> with(auto name = new someGUIWidget(myParent))
>>>>>> {
>>>>>>    shown = true;
>>>>>>    focusable = false;
>>>>>>    some_global_function(name);
>>>>>> }
>>>>>
>>>>> Yeh, I was actually just thinking that myself, and was disappointed to 
>>>>> find out it doesn't work.  :-(
>>>>>
>>>>> Looking at the spec it seems that's special to 'if'.   It could be 
>>>>> useful for switch(), with() and synchronized(), but it seems it hasn't 
>>>>> been added.
>>>>>
>>>>> --bb
>>>> Ohhh. That would be nice in switch ... and while...
>>> I was thinking 'while' would have issues, because the condition is 
>>> evaluated multiple times.  So I left it off the list.  Maybe it's not a 
>>> problem though.  Just make it equiv to
>>> {
>>>    typeof(condition()) x;
>>>    while(x = condition()) {
>>>        // do stuff
>>>    }
>>> }
>>>
>>> --bb
>> 
>> This would be inconsistent with if(), which declares the variable to
>> be local to if's scope. BTW, it'd be nice to have the variable
>> declared outside the if block as you proposed for 'with'. I remember a
>> case or two when I wanted that.
>
>No that's not what I meant.  Note the extra block scope _outside_ the 
>while.  That would be silently introduced by the transformation.  The 
>scope added is a scope that you have no way of interacting with or 
>introducing code into, so effectively it *is* limiting the var scope to 
>the scope of the while().  Of course there are no "scopes" anyway after 
>everything gets compiled down to ASM, so its all just pleasant fictions 
>to help us poor humans understand what's going on.
>
>--bb

 I understand now. But in your second proposal you want the object to
be accessible outside the 'with' block, so would it better to declare
the variable outside the scope in the first place? 

with(auto name = new someGUIWidget(myParent))
{
  shown = true;
  focusable = false;
  some_global_function(name);
}

name.shown = false;