http://d.puremagic.com/issues/show_bug.cgi?id=1060

           Summary: inout in arguments breaks the lvalueness of function
           Product: D
           Version: 1.009
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: gavrilyak@gmail.com


int[] foo(int[] arr){
  return arr;
}

int[] boo(inout int[] arr){
  return arr;
}

int[] arr = [1,2,3];

foo(foo(arr)); // ok
boo(boo(arr)); // Error: boo(arr) is not an lvalue


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1060


fvbommel@wxs.nl changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID




------- Comment #1 from fvbommel@wxs.nl  2007-03-13 17:30 -------
(In reply to comment #0)
> int[] foo(int[] arr){
>   return arr;
> }
> 
> int[] boo(inout int[] arr){
>   return arr;
> }
> 
> int[] arr = [1,2,3];
> 
> foo(foo(arr)); // ok
> boo(boo(arr)); // Error: boo(arr) is not an lvalue

Inout arguments don't "break" the lvalueness of a function. In fact, functions
aren't lvalues, nor are their return values (which is presumably what you
actually meant).
The problem isn't that lvalueness is "broken", it's that an inout argument
requires an lvalue to be passed and you're not doing it (in either case).
Because of that, the second case doesn't work. The first one works fine because
the parameter to foo isn't required to be an lvalue.

Summary: the problem is in your code, not in the compiler or language.

If this explanation isn't clear enough, please post a question about this in digitalmars.D.learn about this. Maybe someone there can explain it better.


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1060


gavrilyak@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED




------- Comment #2 from gavrilyak@gmail.com  2007-03-14 15:19 -------
Thanks for explanation, it's clear. That's how it's supposed to work and C++
works same way too, though it looks like premature optimization.
For me semantics of those 2 snippets is the same
int[] boo(inout int[] arr){
  return arr;
}

int[] arr = [1,2,3];
//first - works
int[] temp = boo(arr);
boo(temp);
//second
boo(boo(arr));


May be D can be less restrictive then C++ and this issue is just a feature request :-).


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=1060


Andrei Alexandrescu <andrei@erdani.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|CLOSED                      |RESOLVED
                 CC|                            |andrei@erdani.com


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