• d-bugmail puremagic.com Mar 13 2007
• d-bugmail puremagic.com Mar 13 2007
• d-bugmail puremagic.com Mar 14 2007

d-bugmail puremagic.com writes:

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


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d-bugmail puremagic.com writes:

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.


-- 

d-bugmail puremagic.com writes:

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 :-).


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