So what does (inout int = 0) do?

[Steven Schveighoffer via Digitalmars-d]

On 4/15/16 3:48 PM, Timon Gehr wrote:
> On 15.04.2016 17:22, Steven Schveighoffer wrote:
>> On 4/14/16 11:10 PM, Andrei Alexandrescu wrote:
>>> Consider:
>>>
>>> https://github.com/D-Programming-Language/phobos/blob/master/std/range/primitives.d#L152
>>>
>>>
>>
>> It works around a limitation of inout that isn't necessary (even though
>> I thought it was being helpful when I suggested it). That is, functions
>> without inout parameters cannot declare local inout variables. But this
>> isn't really necessary, and should be fixed. I will discuss this in my
>> talk in a few weeks.
>> ...
>
> That's potentially dangerous. What about cases like the following?
>
> void main(){
>      inout(int)[] x=[1,2,3];
>      immutable(int) a;
>      int b;
>      inout(int)[] foo(inout int){
>          return x;
>      }
>      immutable(int)[] y=foo(a);
>      int[] z=foo(b);
> }

We don't need to guess:

void foo (inout int)
{
     inout(int)[] x=[1,2,3];
     immutable(int) a;
     int b;
     inout(int)[] foo(inout int){
         return x;
     }
     immutable(int)[] y=foo(a); // line 9
     int[] z=foo(b);  // line 10
}

testinout.d(9): Error: modify inout to immutable is not allowed inside 
inout function
testinout.d(10): Error: modify inout to mutable is not allowed inside 
inout function

>
>
>
>> Note, the =0 part isn't necessary right now, since it's not called. It's
>> just used to test if the function can compile.
>>
>> In short, my opinion on inout is that it has some unnecessary
>> limitations, which can be removed, and inout will work as mostly
>> expected. These requirements to work around the limitations will go away.
>> ...
>
> Other important limitations of inout are e.g.:
> - inout variables cannot be fields.

I have a way to make this work. This is actually the most major sticking 
point in inout.

The only correct thing is to keep is that globals/static variables 
cannot be typed inout.

> - There can be only one inout in scope.

This is not so much a problem I think.

-Steve