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

[Bill Baxter]

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