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digitalmars.D.bugs - [Issue 8788] New: The super constructor call can be prevented by mentioning "return".

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8788

           Summary: The super constructor call can be prevented by
                    mentioning "return".
           Product: D
           Version: D1 & D2
          Platform: x86_64
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: david.eckardt sociomantic.com


--- Comment #0 from David Eckardt <david.eckardt sociomantic.com> 2012-10-09
07:20:46 PDT ---
Mentioning a "return" prevents DMD from rejecting code where a constructor has
an explicit super() call which is done conditionally or not at all. Also it is
possible to return or throw before doing the super() call.
This example code compiles although it should be rejected:
---
class A { this ( ) { } }

class B : A
{
    this ( )
    {
        return;
        super();
    }

    this(int x)
    {
        try
        {
            throw new Exception;
            super();
        }
        catch ( ) { }
    }

    this(float f)
    {
        if (x == 3)
            return;
        else
            super();
    }


    this(char c)
    {
        if (c == 'x')
            super();
        else
            return;
    }
}
---
However, if the "return" statement in the second and third constructor is
omitted, the compile error is triggered correctly.

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next sibling parent d-bugmail puremagic.com writes:
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--- Comment #1 from David Eckardt <david.eckardt sociomantic.com> 2012-10-09
07:27:39 PDT ---
Of course the "if" condition in the third constructor should be f >= 3, not x
== 3.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8788


Don <clugdbug yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |clugdbug yahoo.com.au


--- Comment #2 from Don <clugdbug yahoo.com.au> 2012-10-10 02:58:34 PDT ---
statement.c, ReturnStatement::semantic() contains this comment:

   /* BUG: need to issue an error on:
     *  this
     *  {   if (x) return;
     *      super();
     *  }
     */
Funny that this never got entered in Bugzilla before. The bug however is in the
treatment of CSXreturn, mainly in scope.c.

For each branch of code there are 5 cases:
1. neither constructor calls nor returns have been made.
2. at least one subbranch has returned without calling a constructor.
3. all subbranches have called a constructor. Some may have returned
afterwards, but at least one has not returned yet.
4. all subbranches have exited after calling a constructor
5. some subbranches have returned after calling a constructor, the others have
not yet made constructor calls.


The case with the 'throw' is more difficult than the others. Ideally the first
example below would be OK but the second would be an error:

  try {
    thow SomeFunkyException;
  }
  catch (SomeFunkyException) {
      super();
  }

  try {
    thow SomeFunkyException;
  }
  catch (DifferentFunkyException) {
      super();
  }
It might be worth forbidding 'super()' inside catch clauses.

I don't think it's worth the effort. But the 'return' cases should be detected.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #3 from github-bugzilla puremagic.com 2012-10-20 15:51:36 PDT ---
Commit pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/ecfb19e7d602594db174d9670416916b14b38466
Fix bug 8788 The super constructor call can be prevented by mentioning "return"

Fixes the flow analysis by clearly distinguishing "ALL branches have called a
constructor" from "ANY branches have called a ctor".
There are a large number of special cases.

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prev sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla digitalmars.com
         Resolution|                            |FIXED


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