string <-> null/bool implicit conversion

[Steven Schveighoffer via Digitalmars-d]

On 8/20/15 2:49 PM, Timon Gehr wrote:
> On 08/20/2015 08:05 PM, H. S. Teoh via Digitalmars-d wrote:
>> On Thu, Aug 20, 2015 at 01:50:11PM -0400, Steven Schveighoffer via
>> Digitalmars-d wrote:
>> [...]
>>> The main reason why it caused issues is this nice idiom:
>>>
>>> if(auto arr = someFunction())
>>> {
>>>     // use arr
>>> }
>>>
>>> This would HAVE to be split out to two statements, and the arr variable
>>> would be scoped outside of the if statement.
>> [...]
>>
>> I wish the language would accept:
>>
>>     if ((auto arr = someFunction()) !is null)
>>     {
>>         ...
>>     }
>>
>> But IIRC, auto cannot be used except at the top level expression.
>> ...
>
> You want !=, not !is.
>

Current behavior of if(auto arr = someFunction()) is to compare both 
pointer and length to 0, i.e. !is null.

His point is that if we could get rid of if(arr), then there would at 
least be a way to update existing (correct) code that doesn't involve 
refactoring if the given syntax was accepted.

This also would be acceptable (since not much code ever creates arrays 
with null pointer but non-zero length):

if((auto arr = someFunction()).ptr)

-Steve