Thread overview | |||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
April 28, 2012 cannot cast | ||||
---|---|---|---|---|
| ||||
I finished my Ref/NotNull struct, but i've got a problem: If i try to cast the class, which should implicit convert to Ref!(Type) with alias this, i get the following error message: "cannot cast a1.getRef("Ref.d",72u) of type Ref!(A) to type RefTest.Ref.__unittest1.B" Can someone explain that to me or help me with it? It seems that alias this replacement isn't smart enough to distinguish, if it has to convert. [code] import std.conv : to; struct Ref(T : Object) { private: T _obj; public: @disable this();// { } @disable this(typeof(null));// { } this(T obj) { assert(obj !is null, "Object is null!"); this._obj = obj; } @property inout(T) access() inout { assert(this._obj !is null, "Access: Object is null!"); return this._obj; } //alias access this; // print "Stackoverflow" or "recursive expansion" } mixin template TRef(T : Object) { final Ref!(T) getRef(string file = __FILE__, size_t line = __LINE__) in { assert(this !is null, "Object is null! @ " ~ file ~ " in Line " ~ to!(string)(line) ~ "."); } body { return Ref!(T)(this); } final Ref!(const T) getRef(string file = __FILE__, size_t line = __LINE__) const in { assert(this !is null, "Object is null! @ " ~ file ~ " in Line " ~ to!(string)(line) ~ "."); } body { return Ref!(const T)(this); } alias getRef this; } unittest { class A { mixin TRef!(A); } class B : A { } class C : B { } A a1 = new B(); A a2 = new C(); B b1 = cast(B) a1; // line 72 } |
April 28, 2012 Re: cannot cast | ||||
---|---|---|---|---|
| ||||
Posted in reply to Namespace | On Saturday, 28 April 2012 at 14:21:32 UTC, Namespace wrote:
> I finished my Ref/NotNull struct, but i've got a problem:
> If i try to cast the class, which should implicit convert to Ref!(Type) with alias this, i get the following error message:
> "cannot cast a1.getRef("Ref.d",72u) of type Ref!(A) to type RefTest.Ref.__unittest1.B"
>
> Can someone explain that to me or help me with it?
> It seems that alias this replacement isn't smart enough to distinguish, if it has to convert.
>
> [code]
> import std.conv : to;
>
> struct Ref(T : Object) {
> private:
> T _obj;
>
> public:
> @disable
> this();// { }
>
> @disable
> this(typeof(null));// { }
>
> this(T obj) {
> assert(obj !is null, "Object is null!");
>
> this._obj = obj;
> }
>
> @property
> inout(T) access() inout {
> assert(this._obj !is null, "Access: Object is null!");
>
> return this._obj;
> }
>
> //alias access this; // print "Stackoverflow" or "recursive expansion"
> }
>
> mixin template TRef(T : Object) {
> final Ref!(T) getRef(string file = __FILE__, size_t line = __LINE__) in {
> assert(this !is null, "Object is null! @ " ~ file ~ " in Line " ~ to!(string)(line) ~ ".");
> } body {
> return Ref!(T)(this);
> }
>
> final Ref!(const T) getRef(string file = __FILE__, size_t line = __LINE__) const in {
> assert(this !is null, "Object is null! @ " ~ file ~ " in Line " ~ to!(string)(line) ~ ".");
> } body {
> return Ref!(const T)(this);
> }
>
> alias getRef this;
> }
>
> unittest {
>
> class A {
> mixin TRef!(A);
> }
>
> class B : A { }
>
> class C : B { }
>
> A a1 = new B();
> A a2 = new C();
>
> B b1 = cast(B) a1; // line 72
> }
Trying to fix it with an opCast in Ref ended in an infinity loop...
|
April 28, 2012 alias this : cast turns into endless loop | ||||
---|---|---|---|---|
| ||||
Posted in reply to Namespace | Trying with U opCast(U : Object)() { return new U(); } work fine. It isn't a solution, but i don't understand why this works and the following not: U opCast(U : Object)() { return cast(U) this._obj; } I hope really some of you can explain that to me and help me to fix it. And forgive me the old senseless thread title. ;) |
April 29, 2012 Re: cannot cast | ||||
---|---|---|---|---|
| ||||
Posted in reply to Namespace | On Saturday, 28 April 2012 at 14:21:32 UTC, Namespace wrote: > I finished my Ref/NotNull struct, but i've got a problem: > If i try to cast the class, which should implicit convert to Ref!(Type) with alias this, i get the following error message: > "cannot cast a1.getRef("Ref.d",72u) of type Ref!(A) to type RefTest.Ref.__unittest1.B" I would consider this a bug: http://d.puremagic.com/issues/show_bug.cgi?id=8001 |
April 29, 2012 Re: cannot cast | ||||
---|---|---|---|---|
| ||||
Posted in reply to Jesse Phillips | On Sunday, 29 April 2012 at 14:40:55 UTC, Jesse Phillips wrote:
> On Saturday, 28 April 2012 at 14:21:32 UTC, Namespace wrote:
>> I finished my Ref/NotNull struct, but i've got a problem:
>> If i try to cast the class, which should implicit convert to Ref!(Type) with alias this, i get the following error message:
>> "cannot cast a1.getRef("Ref.d",72u) of type Ref!(A) to type RefTest.Ref.__unittest1.B"
>
> I would consider this a bug:
>
> http://d.puremagic.com/issues/show_bug.cgi?id=8001
Oh, that could explain a lot. Some workaround until now?
|
May 02, 2012 Re: cannot cast | ||||
---|---|---|---|---|
| ||||
Posted in reply to Namespace | Can anyone tell me, why the this code [code] module RefTest.Ref; import std.stdio : writeln; import std.conv : to, toImpl; T const_cast(T : Object)(const T obj) { return cast(T) obj; } struct Ref(T : Object) { private: T _obj; public: @disable this();// { } @disable this(typeof(null));// { } this(T obj) { assert(obj !is null, "Object is null!"); this._obj = obj; } @property inout(T) access() inout { assert(this._obj !is null, "Access: Object is null!"); return this._obj; } //alias access this; // dann kommt "Stackoverflow" oder "recursive expansion" } mixin template TRef(T : Object) { final Ref!(T) getRef(string file = __FILE__, size_t line = __LINE__) in { assert(this !is null, "Object is null! @ " ~ file ~ " in Line " ~ to!(string)(line) ~ "."); } body { return Ref!(T)(this); } final Ref!(const T) getRef(string file = __FILE__, size_t line = __LINE__) const in { assert(this !is null, "Object is null! @ " ~ file ~ " in Line " ~ to!(string)(line) ~ "."); } body { return Ref!(const T)(this); } U opCast(U : Object)() { return *(cast(U*) &this); } alias getRef this; } unittest { bool instanceof(T : Object, U : Object)(const Ref!U obj) { //return const_cast(obj.access).toString() == typeid(T).toString(); const U o = obj.access; return const_cast(o).toString() == typeid(T).toString(); } class A { mixin TRef!(A); } class B : A { } class C : B { } A a1 = new B(); A a2 = new C(); assert(instanceof!(A)(a1) == false); assert(instanceof!(B)(a1)); assert(instanceof!(C)(a1) == false); writeln(a1); B b1 = cast(B) a1; writeln(b1); writeln(); } [/code] fails with: [quote] Fehler 3 instantiated from here: instanceof!(A,A) D:\D\VisualD\Visual Studio 2010\Projects\RefTest\RefTest\Ref.d 76 Fehler 2 Error: template instance RefTest.Ref.const_cast!(A) error instantiating D:\D\VisualD\Visual Studio 2010\Projects\RefTest\RefTest\Ref.d 62 Fehler 4 Error: template instance RefTest.Ref.__unittest1.instanceof!(A,A) error instantiating D:\D\VisualD\Visual Studio 2010\Projects\RefTest\RefTest\Ref.d 76 Fehler 1 Error: function RefTest.Ref.__unittest1.A.TRef!(A).opCast!(A).opCast () is not callable using argument types () D:\D\VisualD\Visual Studio 2010\Projects\RefTest\RefTest\Ref.d 7 [/quote] ? Sounds like a bug. |
May 02, 2012 Re: cannot cast | ||||
---|---|---|---|---|
| ||||
Posted in reply to Namespace | Other, shorter example: [code] import std.stdio, std.traits; class A { int val; alias val this; T opCast(T : Object)() { writeln("FOO"); return to!(T)(this); } } class B : A { } T to(T : Object, U : Object)(const U obj) { return *(cast(T*) &obj); } T const_cast(T)(const T 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); const B b3 = cast(B) a; B b4 = const_cast(b3); } [/code] print: alias_this_impl.d(24): Error: function alias_this_impl.A.opCast!(B).opCast () is not callable using argument types () alias_this_impl.d(44): Error: template instance alias_this_impl.const_cast!(B) e rror instantiating I'm not very skillful in such "template" stories. Maybe someone can help me? |
May 03, 2012 Re: cannot cast | ||||
---|---|---|---|---|
| ||||
Posted in reply to Namespace | On Wednesday, 2 May 2012 at 22:38:36 UTC, Namespace wrote:
> Other, shorter example:
>
> [code]
> import std.stdio, std.traits;
>
> class A {
> int val;
>
> alias val this;
>
> T opCast(T : Object)() {
> writeln("FOO");
>
> return to!(T)(this);
> }
> }
>
> class B : A {
>
> }
>
> T to(T : Object, U : Object)(const U obj) {
> return *(cast(T*) &obj);
> }
>
> T const_cast(T)(const T 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);
>
> const B b3 = cast(B) a;
>
> B b4 = const_cast(b3);
> }
> [/code]
>
> print:
>
> alias_this_impl.d(24): Error: function alias_this_impl.A.opCast!(B).opCast () is
> not callable using argument types ()
> alias_this_impl.d(44): Error: template instance alias_this_impl.const_cast!(B) e
> rror instantiating
>
> I'm not very skillful in such "template" stories. Maybe someone can help me?
Solved with
T const_cast(T)(const T obj) {
return to!(T)(obj);
}
But i think that there must exist a more nicer way to cast away const, isn't there?
To cast away "const" with a simple cast to "T" fails (see my post above), because i have no idea, how i can restrict my opCast. So i have to convert it again with "to". Do some of you have any ideas how i can restrict my opCast, so my const_cast doesn't match it, e.g. with some template magic?
|
May 03, 2012 Re: cannot cast | ||||
---|---|---|---|---|
| ||||
Posted in reply to Namespace | On Thu, 03 May 2012 00:38:35 +0200, Namespace <rswhite4@googlemail.com> wrote:
> I'm not very skillful in such "template" stories. Maybe someone can help me?
The main problem here is your opCast is non-const. (it's always an indication of
const problems when DMD says "<X> is not callable using argument types ()")
Solution:
class A {
int val;
alias val this;
T opCast(T : Object)() {
writeln("FOO");
return to!(T)(this);
}
// Add this
T opCast(T : Object)() const {
writeln("FOO");
return to!(T)(this);
}
}
|
May 03, 2012 Re: cannot cast | ||||
---|---|---|---|---|
| ||||
Posted in reply to Namespace | On Thursday, May 03, 2012 09:33:01 Namespace wrote: > On Wednesday, 2 May 2012 at 22:38:36 UTC, Namespace wrote: > > Other, shorter example: > > > > [code] > > import std.stdio, std.traits; > > > > class A { > > > > int val; > > > > alias val this; > > > > T opCast(T : Object)() { > > > > writeln("FOO"); > > > > return to!(T)(this); > > > > } > > > > } > > > > class B : A { > > > > } > > > > T to(T : Object, U : Object)(const U obj) { > > > > return *(cast(T*) &obj); > > > > } > > > > T const_cast(T)(const T 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); > > > > const B b3 = cast(B) a; > > > > B b4 = const_cast(b3); > > > > } > > [/code] > > > > print: > > > > alias_this_impl.d(24): Error: function > > alias_this_impl.A.opCast!(B).opCast () is > > > > not callable using argument types () > > > > alias_this_impl.d(44): Error: template instance > > alias_this_impl.const_cast!(B) e > > rror instantiating > > > > I'm not very skillful in such "template" stories. Maybe someone can help me? > > Solved with > > T const_cast(T)(const T obj) { > return to!(T)(obj); > } > > But i think that there must exist a more nicer way to cast away const, isn't there? > > To cast away "const" with a simple cast to "T" fails (see my post above), because i have no idea, how i can restrict my opCast. So i have to convert it again with "to". Do some of you have any ideas how i can restrict my opCast, so my const_cast doesn't match it, e.g. with some template magic? If you want to restrict opCast, then use a template constraint, constraining it to what you want to work with it. Also, casting away const is generally a bad idea in D. Casting away const and mutating a variable is an _extremely_ bad idea. You _really_ shouldn't be doing it. So, the fact that you _have_ a function which is specifically trying to cast away const is almost certainly _not_ a good idea. http://stackoverflow.com/questions/4219600/logical-const-in-d - Jonathan M Davis |
Copyright © 1999-2021 by the D Language Foundation