Call site 'ref'

[Timon Gehr]

On 01/16/2012 08:31 AM, Alex Rønne Petersen wrote:
> On 16-01-2012 02:37, Mail Mantis wrote:
>> 2012/1/15 Alex Rønne Petersen<xtzgzorex at gmail.com>:
>>> 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?
>>>
>>> --
>>> - Alex
>>
>> I don't see how call cite ref will help the issue. If you don't read
>> ddoc, how will you know what exactly function does with it's ref
>> parameter - statistically? Knowing that function takes parameter by
>> ref doesn't help understanding it's logic. Also, knowing that function
>> doesn't take any ref parameters doesn't mean you don't need to read
>> it's documentation.
>
> You may remember what the function does, but forget that it mutates an
> input parameter.
>
> --
> - Alex

This statement is self-contradictory.