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April 29, 2012 [Issue 8001] New: Alias this takes ownership of explicit cast | ||||
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http://d.puremagic.com/issues/show_bug.cgi?id=8001 Summary: Alias this takes ownership of explicit cast Product: D Version: D2 Platform: All OS/Version: All Status: NEW Severity: normal Priority: P2 Component: DMD AssignedTo: nobody@puremagic.com ReportedBy: Jesse.K.Phillips+D@gmail.com --- Comment #0 from Jesse Phillips <Jesse.K.Phillips+D@gmail.com> 2012-04-29 07:41:14 PDT --- When attempting to downcast a class which uses alias this, the operation fails because the cast is applied to the item aliased. I think the semantics should be to attempt an implicit cast (alias this), then a cast of the top class, afterwards the alias this item can be casted. test.d(3): Error: e2ir: cannot cast a.val of type int to type test.B void main () { A a = new B(); B b = cast(B) a; } class A { int val; alias val this; } class B : A {} -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- |
May 02, 2012 Re: [Issue 8001] New: Alias this takes ownership of explicit cast | ||||
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Posted in reply to Jesse Phillips | On Sunday, 29 April 2012 at 14:40:06 UTC, Jesse Phillips wrote:
> http://d.puremagic.com/issues/show_bug.cgi?id=8001
>
> Summary: Alias this takes ownership of explicit cast
> Product: D
> Version: D2
> Platform: All
> OS/Version: All
> Status: NEW
> Severity: normal
> Priority: P2
> Component: DMD
> AssignedTo: nobody@puremagic.com
> ReportedBy: Jesse.K.Phillips+D@gmail.com
>
>
> --- Comment #0 from Jesse Phillips <Jesse.K.Phillips+D@gmail.com> 2012-04-29 07:41:14 PDT ---
> When attempting to downcast a class which uses alias this, the operation fails
> because the cast is applied to the item aliased.
>
> I think the semantics should be to attempt an implicit cast (alias this), then
> a cast of the top class, afterwards the alias this item can be casted.
>
> test.d(3): Error: e2ir: cannot cast a.val of type int to type test.B
>
> void main () {
> A a = new B();
> B b = cast(B) a;
> }
>
> class A {
> int val;
> alias val this;
> }
> class B : A {}
Workaround:
import std.stdio;
class A {
int val;
alias val this;
}
class B : A { }
void main () {
A a = new B();
B* b = cast(B*) &a;
}
But i have no idea how this can work implicit as long as this bug isn't fixed.
Maybe it can work with an opCast in B, which cast first to B* and then to B.
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May 02, 2012 Re: [Issue 8001] New: Alias this takes ownership of explicit cast | ||||
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Posted in reply to Namespace | This works fine: [code] import std.stdio; class A { int val; alias val this; T opCast(T : Object)() { return to!(T)(this); } } class B : A { } T to(T : Object, U : Object)(const U obj) { return *(cast(T*) &obj); } void main () { A a = new B(); a.val = 42; writefln("a.val: %d", a.val); B* b = cast(B*) &a; writefln("*b.val: %d", b.val); B b1 = to!(B)(a); writefln("b1.val: %d", b1.val); B b2 = cast(B) a; writefln("b2.val: %d", b2.val); } [/code] |
February 05, 2013 [Issue 8001] Alias this takes ownership of explicit cast | ||||
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Posted in reply to Jesse Phillips | http://d.puremagic.com/issues/show_bug.cgi?id=8001 Maksim Zholudev <maximzms@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |maximzms@gmail.com --- Comment #1 from Maksim Zholudev <maximzms@gmail.com> 2013-02-05 07:57:31 PST --- May be connected with http://d.puremagic.com/issues/show_bug.cgi?id=6777 -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- |
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