[Issue 7019] New: implicit constructors are inconsistently allowed

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=7019

           Summary: implicit constructors are inconsistently allowed
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: mrmocool at gmx.de


--- Comment #0 from Trass3r <mrmocool at gmx.de> 2011-11-26 16:09:09 PST ---
Yes, I'm aware that alias this makes it possible to allow implicit conversions,
but it can't solve everything, esp. if you need to modify the value before you
'save' it:

import std.stdio;
struct A
{
    int store;
    this(int a)
    {
        store = a << 3;
        //...
    }
}

void main()
{
    A a = 5; // this compiles fine
    writeln(a.store); // prints 40

    // but it doesn't work on function calls
    foo(5); // Error: cannot implicitly convert expression (5) of type int to A
}

// nor does it work at global scope or on struct/class fields
A a = 5; // Error: cannot implicitly convert expression (5) of type int to A

void foo(A a) {}


This is horribly and incomprehensibly inconsistent.

btw, if somebody is able to come up with a serious reason why these shouldn't
be allowed in general, I suggest to introduce @implicit.

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