www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.bugs - [Issue 10013] New: `inout` constructor sometimes fails to create immutable object

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=10013

           Summary: `inout` constructor sometimes fails to create
                    immutable object
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: verylonglogin.reg gmail.com


--- Comment #0 from Denis Shelomovskij <verylonglogin.reg gmail.com> 2013-04-30
16:34:45 MSD ---
---
class C
{
    this() inout { }
    this(inout int[]) inout {  }
}

void main()
{
    auto c0 = new immutable C(cast(immutable int[]) null); // OK
    auto c1 = new immutable C(); // Error (line 10)
    auto c2 = new immutable C(null); // Error (line 11)
}
---

dmd output:
---
main.d(10): Error: inout constructor main.C.this creates inout object, not
immutable
main.d(11): Error: inout constructor main.C.this creates mutable object, not
immutable
---

Partial workaround:
Mark constructor as `pure` or `immutable` if possible.

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
Apr 30 2013
parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=10013



--- Comment #1 from Kenji Hara <k.hara.pg gmail.com> 2013-05-04 01:09:08 PDT ---
These are the designed behavior.

1. If the inout constructor has inout parameters, the created object is
restricted to the argument qualifiers - it is same as normal inout functions.
So:

    auto c0 = new immutable C(cast(immutable int[]) null); // OK

constructor call creates inout object and it is implicitly translated to
immutable by the immutable arguments.

1.5 'null' literal is normally treated as a mutable data, so

    auto c2 = new immutable C(null); // Error (line 11)

constructor call creates mutable C object, but it is not convertible to
immutable.


2. To convert the created object to any qualifier, the constructor should have
'pure' attribute at least. So:

    auto c1 = new immutable C(); // Error (line 10)

fails to compile.

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
May 04 2013