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digitalmars.D.bugs - [Issue 2701] New: Can't declare struct, assign lvalue to it in same statement

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2701

           Summary: Can't declare struct, assign lvalue to it in same
                    statement
           Product: D
           Version: 2.025
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Keywords: rejects-valid, spec
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: dsimcha yahoo.com


struct Bar {
    uint num;

    Bar opAssign(uint otherNum) {
        num = otherNum;
        return this;
    }
}

void main() {
    uint foo = 1;
    Bar bar = foo;  // Error:  e2ir:  cannot cast from uint to Bar.
    Bar bar2;
    bar2 = foo;   // Works.
}

Not sure if this is actually a valid bug, since the spec states that "The
assignment operator cannot be overloaded for rvalues that can be implicitly
cast to the lvalue type."  However, if the previous sentence does implicitly
disallow this from working, it should be stated more clearly, instead of in a
single sentence of language legalese.


-- 
Mar 01 2009
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2701





------- Comment #1 from daniel.keep+d.puremagic.com gmail.com  2009-03-01 20:59
-------
You can't use opAssign for initialisation; you have to use opCall. 
Specifically,

Bar bar = foo;

is rewritten as:

Bar bar = Bar(foo);

which is further rewritten as:

Bar bar = Bar.opCall(foo);

I'm not sure if this is documented explicitly anywhere; I just remember this
from when it was implemented.


-- 
Mar 01 2009
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2701


David Simcha <dsimcha yahoo.com> changed:

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


--- Comment #2 from David Simcha <dsimcha yahoo.com> 2010-08-15 21:11:33 PDT ---
I'm closing this, since this appears to be what C'tors are for.  The following
example demonstrates.  Perhaps this should be better documented, though.

struct Bar {
    uint num;

    this(uint otherNum) {
        opAssign(otherNum);
    }

    Bar opAssign(uint otherNum) {
        num = otherNum;
        return this;
    }
}

void main() {
    int foo = 1;
    Bar bar = foo;  // Error:  e2ir:  cannot cast from uint to Bar.
    Bar bar2;
    bar2 = foo;   // Works.
}

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