Call site 'ref'

[Peter Alexander]

On 15/01/12 3:19 PM, dsimcha wrote:
> On 1/15/2012 8:36 AM, Alex Rønne Petersen wrote:
>> Hi,
>>
>> I don't know how many times I've made the mistake of passing a local
>> variable to a function which takes a 'ref' parameter. Suddenly, local
>> variables/fields are just mutating out of nowhere, because it's not at
>> all obvious that a function you're calling is taking a 'ref' parameter.
>> This is particularly true for std.utf.decode().
>>
>> Yes, I realize I could look at the function declaration. Yes, I could
>> read the docs too. But that doesn't prevent me from forgetting that a
>> function takes a 'ref' parameter, and then doing the mistake again. The
>> damage is done, and the time is wasted.
>>
>> I think D should allow 'ref' on call sites to prevent these mistakes.
>> For example:
>>
>> string str = ...;
>> size_t pos;
>> auto chr = std.utf.decode(str, ref pos);
>>
>> Now it's much more obvious that the parameter is passed by reference and
>> is going to be mutated.
>>
>> Ideally, this would not be optional, but rather *required*, but I
>> realize that such a change would break a *lot* of code, so that's
>> probably not a good idea.
>>
>> Thoughts?
>>
>
> This would break UFCS severely. The following would no longer work:
>
> auto arr = [1, 2, 3, 4, 5];
> arr.popFront(); // popFront takes arr by ref

Unless it was ignored for UFCS, which is reasonable, since foo.bar() 
looks like it could modify foo whereas bar(foo) doesn't in general.