Re: Trying Multiple Aggregate reduce
On Monday, 31 March 2014 at 22:25:40 UTC, Nordlöw wrote: You can't use reduce with a const seed. This, surely, must be a compiler bug right? /Per Arguably, it's a user bug ;) The user should have provided a non-const seed. *But*, there have been many cases of reduce being made to accept const seeds before, via unqualified copy. This case must have just been a missed one. In any case, I had submitted a re-write for reduce, and it just so happens to support this. So I added your code to the test cases: https://github.com/D-Programming-Language/phobos/pull/2060
Re: Sockets between D and C(++) app
My bad; It returns immutable(char)*. Still won't work with send(); Am I right to supposed the receiving client must handle a ubyte[] as well (C++) ?
Re: Sockets between D and C(++) app
On Wednesday, 2 April 2014 at 00:34:08 UTC, bearophile wrote: char[] rep = "regan\0".dup; s.send(cast(ubyte[])rep); casts are dangerous, because they silently assume you know what you are doing. As first try I suggest you to remove every cast() from your D program, and replace them with to!() or other functions like toStringz. Sometimes this is not the most efficient thing to do, but it's safer, so it's better when you start to learn D. Bye, bearophile Thanks for your reply. As for cast, I seems not to have any option, because to! doesn't work as I would expect it. It would return me an array of numbers, instead of a string; So I kept the cast here, since I certainly know what it's doing -for now-. I generally use immutables, you caught me, here :-). As of main and return, I was not aware we could just ignore them if we didn't need them. I love explicit programming. However, I'm still stuck with toStringz(). Since it returns an immutable(char[]), I can't find how to pass it to Socket.send(), and I do not seem to be able to cast away the immutable :-s Alexandre
Re: Sockets between D and C(++) app
Alexandre L.:
Some comments on your code:
Here's my 'server' code:
int main(string[] args)
{
If you don't need args, then I suggest to not put it as main
argument. So probably this is better (note no int nor return, in
D they are not needed):
void main() {
...
}
int count = s.receiveFrom(recv_buf);
It's better to use immutable here, and infer the type (use
const/immutable everywhere you don't really need to mutate a
variable/argument/field):
immutable count = s.receiveFrom(recv_buf);
char[] test = cast(char[])recv_buf[0..count-1]; // -1 for C
string comp.
writefln("Received: %s\n", test);
char[] rep = "regan\0".dup;
s.send(cast(ubyte[])rep);
casts are dangerous, because they silently assume you know what
you are doing. As first try I suggest you to remove every cast()
from your D program, and replace them with to!() or other
functions like toStringz. Sometimes this is not the most
efficient thing to do, but it's safer, so it's better when you
start to learn D.
Bye,
bearophile
Sockets between D and C(++) app
Hello,
I lately did a minimal udp socket server-client application with
C++, and I've been trying to recreate it with D, after.
I'm able to get the client's request (C++ client) without too
much trouble (after I figured I needed to get it in ubyte[]).
Then I've tried to send the client an answer through send() (then
tried sendTo() ) but none of them work.
Here's my 'server' code:
int main(string[] args)
{
auto s = new UdpSocket();
auto addr = new InternetAddress("127.0.0.1", );
s.setOption(SocketOptionLevel.IP, SocketOption.REUSEADDR, true);
s.bind(addr);
while (true)
{
ubyte[2048] recv_buf;
int count = s.receiveFrom(recv_buf);
char[] test = cast(char[])recv_buf[0..count-1]; // -1 for C
string comp.
writefln("Received: %s\n", test);
char[] rep = "regan\0".dup;
s.send(cast(ubyte[])rep);
}
writeln("End!");
return 0;
}
Then the client tries to get the string in a std::string, hence
why I did input the \0 literal. I'm also fairly new to D, so any
guidance is sure welcomed!
Alexandre
Re: Why is SysTime.init invalid?
On Tuesday, 1 April 2014 at 10:54:41 UTC, Jonathan M Davis wrote: On Tuesday, April 01, 2014 05:35:28 ed wrote: OK, lazy me just read the std.satetime article again. It appears the design is for no invalid values and it is currently a known limitation due to CTFE. --- d_time_nan There is no equivalent. SysTime.init, which has a null TimeZone object, would be the closest, but once CTFE advances to the point that you can new up class objects with it, SysTime.init's timezone will be LocalTime, so don't rely on SysTime.init being invalid. std.datetime in general tries to avoid having any invalid states for any of its types. It's intended that creating such values be impossible. --- I would still like to know if there is a way around this so I can have my struct default init. You can certainly have a struct with a SysTime member, but there's no way for it to use that SysTime without first assigning a valid value to it - at least, not without segfaulting when it tries to use the SysTime in any context which it would use its timezone member. If you really want to have the SysTime be useable in the init value of your struct, then you can make it so that each of its member functions which use the SysTime member check it for validity first (or have a separate bool which indicates whether the SysTime has been assigned to or not), in which case, it could assign something like SysTime(0) to it, which would be the valid equivalent of SysTime.init. Unfortunately, that does add extra overhead, but there isn't any way around it if you want to have the SysTime be used without having the user of the struct assign to it first. It's pretty much the same boat that SysTime itself is in. I could make it so that it checks the timezone for null every time it's used and assign LocalTime to it if it's null, but that adds constant overhead. My decision was that it was better to just live with the fact that SysTime.init is invalid. It's debatable though, as it's a trade-off. - Jonathan M Davis I have changed my code slightly to what you suggest, assigning SysTime(0) if not initialised. It wasn't a big change and works fine. Thanks, ed
Re: How to dynamically call class virtual method dynamically
On Tuesday, 1 April 2014 at 19:52:47 UTC, Steven Schveighoffer
wrote:
On Tue, 01 Apr 2014 15:00:17 -0400, Frustrated
wrote:
On Tuesday, 1 April 2014 at 12:20:06 UTC, Steven Schveighoffer
wrote:
On Tue, 01 Apr 2014 03:31:41 -0400, Frustrated
wrote:
Basically in programming to interfaces I need to decide to
call a virtual method of an object if it exists else call a
final method in the interface:
interface A
{
static final void foo() { ... }
}
class B : A
{
void bar() { ... } // optional
}
class C : B
{
void bar() { ... } // optional
}
void main()
{
A a = new B; // or new C;
// if a.bar exists call it, else call foo
// code should work independent of the classes. (there
might be more)
}
The point of the code is simply to allow the class to
implement bar optionally but provide default behavior with
foo. I need a way to dynamically determine if bar exists and
fall back on foo. This should be possible.
e.g., suppose
class B : A { }
then I would like to b.bar() to actually call A.foo() (since
bar doesn't exist in b).
I guess the exist way would be to create an opDispatch and
have it call foo if bar is passed. This works great and does
everything I need it to except requires adding the code in
the class which I can't have. Also I'm not sure how it would
work with virtual methods.
Detecting whether bar exists can only happen at compile time,
since an instance of A has no mechanism to detect whether it
has bar. D does not have very good runtime introspection,
that would have to be built into the TypeInfo struct (the
mechanism exists to do it, but it has never been used for
that).
You could use this templates, but that would only work if the
type of the derived class is known at compile time.
This problem could easily be solved by virtual methods with
default implementation.
-Steve
It seems logical to me that I should be able to achieve what I
what.
Suppose I have an object cast to it's interface:
A a = new B;
when I call a.This() it will call the method in the interface.
Either This is a virtual method or a final method. Suppose it
is a Final method since if it is virtual there is no problem.
Now suppose B implements That as a virtual method that doesn't
exist in A.
Since a IS a B, That exists in it's vtable. I should be able
to call it:
a.That(); // Calls B's That().
There is no definition for B's vtable according to A. It just
looks like an array of void pointers.
In other words, there's no possible way, without knowing B's
type structure, to know which entry in the vtable is 'That'.
Of course this doesn't work directly because That() is not
part of the interface. Regardless though, it still exists:
(cast(B)a).That(); // Works
Because you have (at runtime) determined that a actually IS a
'B'.
But the only problem is that the cast(B) is required and is a
trick to get the compiler to do what I want.
It's not a "trick", it's a runtime check. It basically is
saying "if a is actually a B, then call B.That, otherwise
segfault"
But we know that a is of type B.
The compiler/runtime does not know that.
e.g., typeof(cast(Object)a) returns B, right?
You are thinking of typeid. But the runtime information does
not contain any way to figure out which location 'That' is at.
What you are really looking for is runtime introspection,
similar to Java or C#. D has the capability, but it has not
been implemented. We only have compile-time introspection.
I could be mistaken but isn't `A a = new B` just a facade and
a really is of type B?
a is of type A, and it points at an instance of B.
If so, isn't there a way to get the true type of a at runtime?
If so, then can't we cast a to its true type at runtime and
access its members properly?
You can get at B's typeinfo, but that doesn't contain a way to
call arbitrarily named functions.
e.g., suppose truecast(a) returns a as the actual object that
a was created as(in this case B, not A). Then
truecast(a).That() would work.
With the correct implementation of RTInfo inside object.di, you
could possibly make this work. It would be kind of cool. It
would be a TON of work to make this a reality.
-Steve
Here is a basic outline of a possible approach. I do not believe
it is the best way
import std.stdio, std.cstream;
interface A
{
public final void opDispatch(string m)()
{
opDispatchImpl(m);
}
protected bool opDispatchImpl(string m);
// void bar() { writeln("hello"); } // possible but name
conflict
}
class B : A
{
void bar() { writeln("asdfasdf"); }
override bool opDispatchImpl(string m)
{
if (m == "bar") bar();
return false;
}
}
void main()
{
A a = new B;
B b = new B;
a.bar(); // Wow, A doesn't have a bar yet we call it?!?!
b.bar();
din.getc();
}
Note that a does not have a
Re: template interface and delegates
On Tue, 01 Apr 2014 15:47:42 -0400, anonymous wrote: Is this bug allready reported? or can somebody who has a deeper insight to this report it? I don't know. I think you should report it. If it's already reported, someone will close it as a "duplicate" -Steve
Re: How to dynamically call class virtual method dynamically
On Tue, 01 Apr 2014 15:00:17 -0400, Frustrated wrote:
On Tuesday, 1 April 2014 at 12:20:06 UTC, Steven Schveighoffer wrote:
On Tue, 01 Apr 2014 03:31:41 -0400, Frustrated wrote:
Basically in programming to interfaces I need to decide to call a
virtual method of an object if it exists else call a final method in
the interface:
interface A
{
static final void foo() { ... }
}
class B : A
{
void bar() { ... } // optional
}
class C : B
{
void bar() { ... } // optional
}
void main()
{
A a = new B; // or new C;
// if a.bar exists call it, else call foo
// code should work independent of the classes. (there might be
more)
}
The point of the code is simply to allow the class to implement bar
optionally but provide default behavior with foo. I need a way to
dynamically determine if bar exists and fall back on foo. This should
be possible.
e.g., suppose
class B : A { }
then I would like to b.bar() to actually call A.foo() (since bar
doesn't exist in b).
I guess the exist way would be to create an opDispatch and have it
call foo if bar is passed. This works great and does everything I need
it to except requires adding the code in the class which I can't have.
Also I'm not sure how it would work with virtual methods.
Detecting whether bar exists can only happen at compile time, since an
instance of A has no mechanism to detect whether it has bar. D does not
have very good runtime introspection, that would have to be built into
the TypeInfo struct (the mechanism exists to do it, but it has never
been used for that).
You could use this templates, but that would only work if the type of
the derived class is known at compile time.
This problem could easily be solved by virtual methods with default
implementation.
-Steve
It seems logical to me that I should be able to achieve what I what.
Suppose I have an object cast to it's interface:
A a = new B;
when I call a.This() it will call the method in the interface. Either
This is a virtual method or a final method. Suppose it is a Final method
since if it is virtual there is no problem.
Now suppose B implements That as a virtual method that doesn't exist in
A.
Since a IS a B, That exists in it's vtable. I should be able to call it:
a.That(); // Calls B's That().
There is no definition for B's vtable according to A. It just looks like
an array of void pointers.
In other words, there's no possible way, without knowing B's type
structure, to know which entry in the vtable is 'That'.
Of course this doesn't work directly because That() is not part of the
interface. Regardless though, it still exists:
(cast(B)a).That(); // Works
Because you have (at runtime) determined that a actually IS a 'B'.
But the only problem is that the cast(B) is required and is a trick to
get the compiler to do what I want.
It's not a "trick", it's a runtime check. It basically is saying "if a is
actually a B, then call B.That, otherwise segfault"
But we know that a is of type B.
The compiler/runtime does not know that.
e.g., typeof(cast(Object)a) returns B, right?
You are thinking of typeid. But the runtime information does not contain
any way to figure out which location 'That' is at.
What you are really looking for is runtime introspection, similar to Java
or C#. D has the capability, but it has not been implemented. We only have
compile-time introspection.
I could be mistaken but isn't `A a = new B` just a facade and a really
is of type B?
a is of type A, and it points at an instance of B.
If so, isn't there a way to get the true type of a at runtime? If so,
then can't we cast a to its true type at runtime and access its members
properly?
You can get at B's typeinfo, but that doesn't contain a way to call
arbitrarily named functions.
e.g., suppose truecast(a) returns a as the actual object that a was
created as(in this case B, not A). Then truecast(a).That() would work.
With the correct implementation of RTInfo inside object.di, you could
possibly make this work. It would be kind of cool. It would be a TON of
work to make this a reality.
-Steve
Re: template interface and delegates
Is this bug allready reported? or can somebody who has a deeper insight to this report it? On Tuesday, 1 April 2014 at 05:51:46 UTC, anonymous wrote: Ok, thought i did something wrong or got some wrong idea how it should work.
Re: How to dynamically call class virtual method dynamically
On Tuesday, 1 April 2014 at 19:00:18 UTC, Frustrated wrote: A a = new B; [...] Now suppose B implements That as a virtual method that doesn't exist in A. [...] e.g., typeof(cast(Object)a) returns B, right? No, it's Object. You're looking for typeid which returns a TypeInfo [1] which is runtime information about the type. For classes that's for the most derived one (here: B). I could be mistaken but isn't `A a = new B` just a facade and a really is of type B? If so, isn't there a way to get the true type of a at runtime? If so, then can't we cast a to its true type at runtime and access its members properly? Yes, all true. But you need the target type at compile time to cast. e.g., suppose truecast(a) returns a as the actual object that a was created as(in this case B, not A). Then truecast(a).That() would work. When different implementations of A have different Thats, they are not related in any way. And the compiler doesn't know about (possibly future) implementations when working on code that uses just the interface A. So, as far as I can see, truecast(a).That() would have to be a string lookup at runtime. And then the members' types would be dynamic, too, of course. I have no idea how one would go about that. My best guess is that all of D's type system would have to be duplicated at runtime. [1] http://dlang.org/phobos/object.html#TypeInfo
Re: How to dynamically call class virtual method dynamically
On Tuesday, 1 April 2014 at 12:20:06 UTC, Steven Schveighoffer
wrote:
On Tue, 01 Apr 2014 03:31:41 -0400, Frustrated
wrote:
Basically in programming to interfaces I need to decide to
call a virtual method of an object if it exists else call a
final method in the interface:
interface A
{
static final void foo() { ... }
}
class B : A
{
void bar() { ... } // optional
}
class C : B
{
void bar() { ... } // optional
}
void main()
{
A a = new B; // or new C;
// if a.bar exists call it, else call foo
// code should work independent of the classes. (there
might be more)
}
The point of the code is simply to allow the class to
implement bar optionally but provide default behavior with
foo. I need a way to dynamically determine if bar exists and
fall back on foo. This should be possible.
e.g., suppose
class B : A { }
then I would like to b.bar() to actually call A.foo() (since
bar doesn't exist in b).
I guess the exist way would be to create an opDispatch and
have it call foo if bar is passed. This works great and does
everything I need it to except requires adding the code in the
class which I can't have. Also I'm not sure how it would work
with virtual methods.
Detecting whether bar exists can only happen at compile time,
since an instance of A has no mechanism to detect whether it
has bar. D does not have very good runtime introspection, that
would have to be built into the TypeInfo struct (the mechanism
exists to do it, but it has never been used for that).
You could use this templates, but that would only work if the
type of the derived class is known at compile time.
This problem could easily be solved by virtual methods with
default implementation.
-Steve
It seems logical to me that I should be able to achieve what I
what.
Suppose I have an object cast to it's interface:
A a = new B;
when I call a.This() it will call the method in the interface.
Either This is a virtual method or a final method. Suppose it is
a Final method since if it is virtual there is no problem.
Now suppose B implements That as a virtual method that doesn't
exist in A.
Since a IS a B, That exists in it's vtable. I should be able to
call it:
a.That(); // Calls B's That().
Of course this doesn't work directly because That() is not part
of the interface. Regardless though, it still exists:
(cast(B)a).That(); // Works
But the only problem is that the cast(B) is required and is a
trick to get the compiler to do what I want.
But we know that a is of type B.
e.g., typeof(cast(Object)a) returns B, right?
Basically, it should be very easy for the compiler to internally
cast a object to it's actual type(since that is contained in the
object information, even if it's cast to something else) and call
members on it. Of course, I'm not asking for an internal way.
I could be mistaken but isn't `A a = new B` just a facade and a
really is of type B? If so, isn't there a way to get the true
type of a at runtime? If so, then can't we cast a to its true
type at runtime and access its members properly?
e.g., suppose truecast(a) returns a as the actual object that a
was created as(in this case B, not A). Then truecast(a).That()
would work.
I'm sort of looking for the truecast function/template.
Of course, if D doesn't store information about the actual type
an object is inside it(which it doesn't AFAIK) then you can't
truecast.
Re: How to foreach over a DList?
Just for reference, this is the compiling code: https://gist.github.com/Binero/f30e56351baf05f1a2ec
Re: How to foreach over a DList?
On Tuesday, 1 April 2014 at 15:16:41 UTC, Meta wrote:
On Tuesday, 1 April 2014 at 13:55:05 UTC, monarch_dodra wrote:
On Tuesday, 1 April 2014 at 13:54:00 UTC, monarch_dodra wrote:
In contrast, if you *pass* "1" to the DList, you lose that
info, and the DList will complain that you are trying to
assign an int to a ubyte.
EDIT: The issue is actually one of template constraint, but
it's
essentially equivalent. Without context you can't assign an int
to a ubyte.
I thought that maybe VRP might work here (as you detailed in
your other post), as it works elsewhere. Is is possible to
extend VRP to cover this situation?
*Maybe*, but it would require getting rid of the constraints.
However, those template constraints are necessary to resolve the
overloads to begin with ("insertBack(value)" vs
"insertBack(range)"). So VRP wouldn't even get a chance to
trigger :/
Re: How to foreach over a DList?
On Tuesday, 1 April 2014 at 13:55:05 UTC, monarch_dodra wrote: On Tuesday, 1 April 2014 at 13:54:00 UTC, monarch_dodra wrote: In contrast, if you *pass* "1" to the DList, you lose that info, and the DList will complain that you are trying to assign an int to a ubyte. EDIT: The issue is actually one of template constraint, but it's essentially equivalent. Without context you can't assign an int to a ubyte. I thought that maybe VRP might work here (as you detailed in your other post), as it works elsewhere. Is is possible to extend VRP to cover this situation?
Re: How to foreach over a DList?
On Tue, Apr 01, 2014 at 06:04:48AM +, monarch_dodra wrote: > On Tuesday, 1 April 2014 at 04:43:44 UTC, H. S. Teoh wrote: > >On Mon, Mar 31, 2014 at 09:55:01PM +, monarch_dodra wrote: > >>On Monday, 31 March 2014 at 21:41:16 UTC, H. S. Teoh wrote: > >>>Argh, why is opSlice non-const? :-( Please file a bug. > >> > >>If opSlice was const, then you'd get a const slice, with const > >>reference. You wouldn't even be able to iterate on it. > >[...] > > > >Um... wat? > > I'm pointing out the fix is not as trivial as slapping "const" onto > the signature. It requires a very real investment in terms of > development. [...] Well, yes... I don't expect just adding 'const' to an existing function is going to magically make it work with const types. :-P Though I suppose the way I said it was ambiguous. My bad. T -- Those who don't understand Unix are condemned to reinvent it, poorly.
Re: How to foreach over a DList?
On Tuesday, 1 April 2014 at 13:54:00 UTC, monarch_dodra wrote: In contrast, if you *pass* "1" to the DList, you lose that info, and the DList will complain that you are trying to assign an int to a ubyte. EDIT: The issue is actually one of template constraint, but it's essentially equivalent. Without context you can't assign an int to a ubyte.
Re: How to foreach over a DList?
On Tuesday, 1 April 2014 at 13:30:21 UTC, Meta wrote: On Tuesday, 1 April 2014 at 12:30:03 UTC, monarch_dodra wrote: I fixed this not too long ago. Long story short, the "~=" implementations were made of fail. Just change those "~=" for "insertBack" and you should be fine. That aside, why is it necessary to cast 1, 2 and 3 to ubyte when adding them to the DList? Is this a problem with DList or with D? D has a "feature", where you can't assign something big into something small. EG, you can't assign an int to a byte. This avoids dangerous overflow. That said, this is *usually* transparent, because D *also* has value range analysis. So what this means is that when you write: "ubyte b = 1;" Even though "1" is actually an int, the compiler knows it is int he 0-255 range, so the assignment is fine. In contrast, if you *pass* "1" to the DList, you lose that info, and the DList will complain that you are trying to assign an int to a ubyte. For what it's worth, 2.066 introduces uniform initialization, so this will become valid, and is somewhat less intrusive: list1.insertBack(ubyte(1)); list1.insertBack(ubyte(2)); list1.insertBack(ubyte(3));
Re: How to foreach over a DList?
On Tue, 01 Apr 2014 09:30:18 -0400, Meta wrote: On Tuesday, 1 April 2014 at 12:30:03 UTC, monarch_dodra wrote: I fixed this not too long ago. Long story short, the "~=" implementations were made of fail. Just change those "~=" for "insertBack" and you should be fine. That aside, why is it necessary to cast 1, 2 and 3 to ubyte when adding them to the DList? Is this a problem with DList or with D? A limitation with D. The issue is that IFTI interprets numeric literals as type int. There simply is no way to say "if you get a numeric literal that fits within a ubyte, use ubyte as the type for T" See this bug report: http://d.puremagic.com/issues/show_bug.cgi?id=4998 -Steve
Re: How to foreach over a DList?
On Tuesday, 1 April 2014 at 12:30:03 UTC, monarch_dodra wrote: I fixed this not too long ago. Long story short, the "~=" implementations were made of fail. Just change those "~=" for "insertBack" and you should be fine. That aside, why is it necessary to cast 1, 2 and 3 to ubyte when adding them to the DList? Is this a problem with DList or with D?
Re: How to foreach over a DList?
On Tuesday, 1 April 2014 at 10:56:40 UTC, Ali Çehreli wrote:
On 03/31/2014 10:32 PM, Jeroen Bollen wrote:
Still no luck:
import std.container;
import std.stdio;
void main()
{
DList!ubyte list1 = DList!ubyte();
list1 ~= cast(ubyte) 1;
list1 ~= cast(ubyte) 2;
list1 ~= cast(ubyte) 3;
foreach(ubyte item; list1[]) {
writeln(item);
}
}
/usr/include/dlang/dmd/std/container.d(1874): Error: no
property
'_first' for type 'ubyte'
/usr/include/dlang/dmd/std/container.d(1875): Error: no
property
'_first' for type 'ubyte'
/usr/include/dlang/dmd/std/container.d(1875): Error: undefined
identifier rhs_, did you mean variable rhs?
source/app.d(7): Error: template instance
std.container.DList!ubyte.DList.opOpAssign!("~", ubyte) error
instantiating
source/app.d(7): Error: cannot append type ubyte to type
DList!ubyte
I think your problem is fixed in a more recent compiler. The
code works with git head dmd but fails with e.g. 2.064. (Not
tested with 2.065.)
Ali
I fixed this not too long ago. Long story short, the "~="
implementations were made of fail.
Just change those "~=" for "insertBack" and you should be fine.
Re: How to dynamically call class virtual method dynamically
On Tue, 01 Apr 2014 03:31:41 -0400, Frustrated wrote:
Basically in programming to interfaces I need to decide to call a
virtual method of an object if it exists else call a final method in the
interface:
interface A
{
static final void foo() { ... }
}
class B : A
{
void bar() { ... } // optional
}
class C : B
{
void bar() { ... } // optional
}
void main()
{
A a = new B; // or new C;
// if a.bar exists call it, else call foo
// code should work independent of the classes. (there might be
more)
}
The point of the code is simply to allow the class to implement bar
optionally but provide default behavior with foo. I need a way to
dynamically determine if bar exists and fall back on foo. This should be
possible.
e.g., suppose
class B : A { }
then I would like to b.bar() to actually call A.foo() (since bar doesn't
exist in b).
I guess the exist way would be to create an opDispatch and have it call
foo if bar is passed. This works great and does everything I need it to
except requires adding the code in the class which I can't have. Also
I'm not sure how it would work with virtual methods.
Detecting whether bar exists can only happen at compile time, since an
instance of A has no mechanism to detect whether it has bar. D does not
have very good runtime introspection, that would have to be built into the
TypeInfo struct (the mechanism exists to do it, but it has never been used
for that).
You could use this templates, but that would only work if the type of the
derived class is known at compile time.
This problem could easily be solved by virtual methods with default
implementation.
-Steve
Re: How to foreach over a DList?
John Colvin: doesn't work on 2.065 But it works in the latest alpha. Bye, bearophile
Re: How to foreach over a DList?
On Tuesday, 1 April 2014 at 10:56:40 UTC, Ali Çehreli wrote:
On 03/31/2014 10:32 PM, Jeroen Bollen wrote:
Still no luck:
import std.container;
import std.stdio;
void main()
{
DList!ubyte list1 = DList!ubyte();
list1 ~= cast(ubyte) 1;
list1 ~= cast(ubyte) 2;
list1 ~= cast(ubyte) 3;
foreach(ubyte item; list1[]) {
writeln(item);
}
}
/usr/include/dlang/dmd/std/container.d(1874): Error: no
property
'_first' for type 'ubyte'
/usr/include/dlang/dmd/std/container.d(1875): Error: no
property
'_first' for type 'ubyte'
/usr/include/dlang/dmd/std/container.d(1875): Error: undefined
identifier rhs_, did you mean variable rhs?
source/app.d(7): Error: template instance
std.container.DList!ubyte.DList.opOpAssign!("~", ubyte) error
instantiating
source/app.d(7): Error: cannot append type ubyte to type
DList!ubyte
I think your problem is fixed in a more recent compiler. The
code works with git head dmd but fails with e.g. 2.064. (Not
tested with 2.065.)
Ali
doesn't work on 2.065
Re: How to foreach over a DList?
On 03/31/2014 10:32 PM, Jeroen Bollen wrote:
Still no luck:
import std.container;
import std.stdio;
void main()
{
DList!ubyte list1 = DList!ubyte();
list1 ~= cast(ubyte) 1;
list1 ~= cast(ubyte) 2;
list1 ~= cast(ubyte) 3;
foreach(ubyte item; list1[]) {
writeln(item);
}
}
/usr/include/dlang/dmd/std/container.d(1874): Error: no property
'_first' for type 'ubyte'
/usr/include/dlang/dmd/std/container.d(1875): Error: no property
'_first' for type 'ubyte'
/usr/include/dlang/dmd/std/container.d(1875): Error: undefined
identifier rhs_, did you mean variable rhs?
source/app.d(7): Error: template instance
std.container.DList!ubyte.DList.opOpAssign!("~", ubyte) error instantiating
source/app.d(7): Error: cannot append type ubyte to type DList!ubyte
I think your problem is fixed in a more recent compiler. The code works
with git head dmd but fails with e.g. 2.064. (Not tested with 2.065.)
Ali
Re: Why is SysTime.init invalid?
On Tuesday, April 01, 2014 05:35:28 ed wrote: > OK, lazy me just read the std.satetime article again. It appears > the design is for no invalid values and it is currently a known > limitation due to CTFE. > > --- > d_time_nanThere is no equivalent. SysTime.init, which has a null > TimeZone object, would be the closest, but once CTFE advances to > the point that you can new up class objects with it, > SysTime.init's timezone will be LocalTime, so don't rely on > SysTime.init being invalid. std.datetime in general tries to > avoid having any invalid states for any of its types. It's > intended that creating such values be impossible. > --- > > I would still like to know if there is a way around this so I can > have my struct default init. You can certainly have a struct with a SysTime member, but there's no way for it to use that SysTime without first assigning a valid value to it - at least, not without segfaulting when it tries to use the SysTime in any context which it would use its timezone member. If you really want to have the SysTime be useable in the init value of your struct, then you can make it so that each of its member functions which use the SysTime member check it for validity first (or have a separate bool which indicates whether the SysTime has been assigned to or not), in which case, it could assign something like SysTime(0) to it, which would be the valid equivalent of SysTime.init. Unfortunately, that does add extra overhead, but there isn't any way around it if you want to have the SysTime be used without having the user of the struct assign to it first. It's pretty much the same boat that SysTime itself is in. I could make it so that it checks the timezone for null every time it's used and assign LocalTime to it if it's null, but that adds constant overhead. My decision was that it was better to just live with the fact that SysTime.init is invalid. It's debatable though, as it's a trade-off. - Jonathan M Davis
Re: How to dynamically call class virtual method dynamically
On Tuesday, 1 April 2014 at 09:12:41 UTC, John Colvin wrote: Also, bear in mind that polymorphism is one-way: you can call base class methods through an inherited class reference, but not the other way around. Sorry, I should clarify that: Given an inheritance tree with the base class class at the bottom, calls can always be made down the tree (inheriting class reference calling method in inherited class), but you can only call up the tree via overriden virtual functions (inherited class reference calling inheriting class functions). A new method that isn't present in the base class is by definition not overriding anything in the base class. Therefore you cannot call it from a base class reference, that would mean moving up the inheritance tree.
Re: How to dynamically call class virtual method dynamically
On Tuesday, 1 April 2014 at 07:31:43 UTC, Frustrated wrote:
Basically in programming to interfaces I need to decide to call
a virtual method of an object if it exists else call a final
method in the interface:
interface A
{
static final void foo() { ... }
}
class B : A
{
void bar() { ... } // optional
}
class C : B
{
void bar() { ... } // optional
}
void main()
{
A a = new B; // or new C;
// if a.bar exists call it, else call foo
// code should work independent of the classes. (there
might be more)
}
The point of the code is simply to allow the class to implement
bar optionally but provide default behavior with foo. I need a
way to dynamically determine if bar exists and fall back on
foo. This should be possible.
e.g., suppose
class B : A { }
then I would like to b.bar() to actually call A.foo() (since
bar doesn't exist in b).
I guess the exist way would be to create an opDispatch and have
it call foo if bar is passed. This works great and does
everything I need it to except requires adding the code in the
class which I can't have. Also I'm not sure how it would work
with virtual methods.
I've tried using hasMember but since my object is cast to a
type of Object it never works.
The traditional OO approach would probably be this:
import std.stdio;
class A
{
static final void foo() { writeln("A.foo"); }
void bar() { foo(); }
}
class B : A
{
override void bar() { writeln("B.bar"); } // optional
}
class C : A {}
void main()
{
A a0 = new B; // or new C;
A a1 = new C; // or new C;
a0.bar(); //B.bar
a1.bar(); //A.foo
}
Also, bear in mind that polymorphism is one-way: you can call
base class methods through an inherited class reference, but not
the other way around.
interface A {}
class B : A
{
void bar() {}
}
void main()
{
A a = new B;
a.bar(); // Error: no property 'bar' for type 'A'
}
How to dynamically call class virtual method dynamically
Basically in programming to interfaces I need to decide to call a
virtual method of an object if it exists else call a final method
in the interface:
interface A
{
static final void foo() { ... }
}
class B : A
{
void bar() { ... } // optional
}
class C : B
{
void bar() { ... } // optional
}
void main()
{
A a = new B; // or new C;
// if a.bar exists call it, else call foo
// code should work independent of the classes. (there might
be more)
}
The point of the code is simply to allow the class to implement
bar optionally but provide default behavior with foo. I need a
way to dynamically determine if bar exists and fall back on foo.
This should be possible.
e.g., suppose
class B : A { }
then I would like to b.bar() to actually call A.foo() (since bar
doesn't exist in b).
I guess the exist way would be to create an opDispatch and have
it call foo if bar is passed. This works great and does
everything I need it to except requires adding the code in the
class which I can't have. Also I'm not sure how it would work
with virtual methods.
I've tried using hasMember but since my object is cast to a type
of Object it never works.
