Re: Rebind template(bug?)
On Monday, 22 August 2016 at 21:46:35 UTC, Engine Machine wrote: I'm sorry if it confuses you... it doesn't confuse me. Confuses? No. I do not know why you have to try and prove something that is a preference. Do you often get in to arguments with people about how ford is better than chevy or blonds are better than brunettes? You're wrong again. I don't try to prove anything, just answer your questions. But finally I understood your main goal: You don't want to see more than one 'class' keyword. You want that recursive class template automatically stops inheritance without any additional moves, such as specializations, static ifs and so on.
Re: Rebind template(bug?)
On 08/23/2016 03:23 AM, Engine Machine wrote: On Monday, 22 August 2016 at 22:52:28 UTC, ag0aep6g wrote: [...] Simply not replying is an option, too. It may be a bit less polite, but it's better than escalating things. True, but then you should also take your own advice. Yeah, I'm going to do that from now on regarding posts of yours.
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 22:52:28 UTC, ag0aep6g wrote: On Monday, 22 August 2016 at 21:46:35 UTC, Engine Machine wrote: I'm sorry if it confuses you... it doesn't confuse me. You needed quite some help to get this thing to work. And you made some mistakes and wrong statements in the process. That's perfectly fine, but please don't act as if Jack is the simpleton while you're the brainiac. Um, please don't be an arrogant prick. I never said anything about that. He says it confuses him, I said it doesn't confuse me. Getting it to work in D has nothing to do with understanding the structure. It's like saying that because you can't understand English that you must be an imbecile. I do not know why you have to try and prove something that is a preference. Jack showed a version which he thinks is "cleaner". And since this is a discussion board about code, it makes perfect sense for him to do that. If you don't care about it, you don't have to engage in discussion, of course. So? I am the one that asked the question how to do X. He brings up Y, then you try to justify Y. It is illogical and insane to do so. Do you often get in to arguments with people about how ford is better than chevy or blonds are better than brunettes? Please don't take this to a personal level. Jack was talking about the code, and you start questioning his character. Not cool. No, Jack is talking about Y and people that try to change topics, like you have done, is insane and do the same thing with what I have stated. Keep it up though. If you're happy with what you got, and you don't want to discuss other versions, you can say so without setting the stage for a shouting match. Simply not replying is an option, too. It may be a bit less polite, but it's better than escalating things. True, but then you should also take your own advice. But if a person can't be direct, honest, and talk specifically what is asked about, then it is already the well is already poisoned. But which will you option will you choose?
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 21:46:35 UTC, Engine Machine wrote: I'm sorry if it confuses you... it doesn't confuse me. You needed quite some help to get this thing to work. And you made some mistakes and wrong statements in the process. That's perfectly fine, but please don't act as if Jack is the simpleton while you're the brainiac. I do not know why you have to try and prove something that is a preference. Jack showed a version which he thinks is "cleaner". And since this is a discussion board about code, it makes perfect sense for him to do that. If you don't care about it, you don't have to engage in discussion, of course. Do you often get in to arguments with people about how ford is better than chevy or blonds are better than brunettes? Please don't take this to a personal level. Jack was talking about the code, and you start questioning his character. Not cool. If you're happy with what you got, and you don't want to discuss other versions, you can say so without setting the stage for a shouting match. Simply not replying is an option, too. It may be a bit less polite, but it's better than escalating things.
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 19:09:34 UTC, Jack Applegame wrote: On Monday, 22 August 2016 at 18:04:43 UTC, Engine Machine wrote: How do you seriously think this is cleaner/simpler? 1. No extra encrypted things, such as InstantiateOrEmptySeq 2. Much more understandable. You have two classes. No. I have one template with two specializations. Class template and class is not the same thing. Their is no uniformity between them. They have the same name. This is the best uniformity. You have uniformity between all the derived classes then have a special case for the base class. A certain easy to follow pattern is set up but needlessly break it for one case. Why? Because it is the base class. It has no parent. Also this is the standard and well known pattern in template metaprogramming. I'm sorry if it confuses you... it doesn't confuse me. I do not know why you have to try and prove something that is a preference. Do you often get in to arguments with people about how ford is better than chevy or blonds are better than brunettes?
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 19:56:08 UTC, ag0aep6g wrote:
So this is just to avoid typing out `class Pug : Dog {...}
class Dog : Animal {...} class Animal {...}`?
This allows you to create different inheritance chains with the
same components quickly and easily. I don't know any use case,
but looks funny:
T!("Animal", "Dog", "Pug") pug1;
T!("Life", "Animal", "Four-legged", "Pug") pug2;
T!("Dog", "Small", "Pug", ) smallPug;
Re: Rebind template(bug?)
On 08/22/2016 08:54 PM, Engine Machine wrote:
Yeah, but a name means nothing. Change it if you want ;)
Even with a better name it still requires a good amount of thinking by
the reader to see what's going on.
[...]
What it achieves is a uniform way to create a hierarchical relationship
without excessive verbosity.
[...]
Ultimately it is just syntax, it does nothing over what D already does.
It doesn't create anything new. In some cases it simplifies. If it does,
then great, if it doesn't then don't use it. While I would prefer a
totally different syntax, I also like to keep things organized. Having
multiple classes floating around for certain things is just not needed
so there should be an option.
So this is just to avoid typing out `class Pug : Dog {...} class Dog :
Animal {...} class Animal {...}`? If so, I don't think it's worth the
hassle. At least in the version so far, it doesn't seem to really cut
down on the typing.
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 18:48:12 UTC, ag0aep6g wrote:
You can take this further with template constraints. Gives it a
more uniform appearance at the price of some repetition:
class T()
{
int x;
}
class T(A...) : T!(A[0..$-1])
if (A.length > 0 && A[$-1] == "Animal")
{
int y;
}
class T(A...) : T!(A[0..$-1])
if (A.length > 0 && A[$-1] == "Dog")
{
int z;
}
class T(A...) : T!(A[0..$-1])
if (A.length > 0 && A[$-1] == "Pug")
{
int s;
}
Yes. And even simpler, if to change the order of template
parameters:
class T() {
int x;
}
class T(string type : "Animal", A...) : T!A {
int y;
}
class T(string type : "Dog", A...) : T!A {
int z;
}
class T(string type : "Pug", A...) : T!A {
int s;
}
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 18:04:43 UTC, Engine Machine wrote: How do you seriously think this is cleaner/simpler? 1. No extra encrypted things, such as InstantiateOrEmptySeq 2. Much more understandable. You have two classes. No. I have one template with two specializations. Class template and class is not the same thing. Their is no uniformity between them. They have the same name. This is the best uniformity. You have uniformity between all the derived classes then have a special case for the base class. A certain easy to follow pattern is set up but needlessly break it for one case. Why? Because it is the base class. It has no parent. Also this is the standard and well known pattern in template metaprogramming.
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 18:48:12 UTC, ag0aep6g wrote:
On 08/22/2016 08:04 PM, Engine Machine wrote:
How do you seriously think this is cleaner/simpler? You have
two
classes. Their is no uniformity between them. You have
uniformity
between all the derived classes then have a special case for
the base
class. A certain easy to follow pattern is set up but
needlessly break
it for one case. Why?
It avoids the relatively obscure (and badly named, by me)
InstantiateOrEmptySeq template.
You can take this further with template constraints. Gives it a
more uniform appearance at the price of some repetition:
class T()
{
int x;
}
class T(A...) : T!(A[0..$-1])
if (A.length > 0 && A[$-1] == "Animal")
{
int y;
}
class T(A...) : T!(A[0..$-1])
if (A.length > 0 && A[$-1] == "Dog")
{
int z;
}
class T(A...) : T!(A[0..$-1])
if (A.length > 0 && A[$-1] == "Pug")
{
int s;
}
I wouldn't say that this is obviously, objectively,
significantly better than the version with the helper template,
though.
Yeah, but a name means nothing. Change it if you want ;)
By the way, it's not obvious to me what this whole thing
achieves in practice. And whatever benefit there is, it has to
be weighed against the cost of the added complexity.
What it achieves is a uniform way to create a hierarchical
relationship without excessive verbosity. Now, the static ifs are
probably the most verbose part, a static switch would help:
static switch (A)
{
case "Animal":
return;
...
}
But only slightly.
I don't mean to say that this is not worth pursuing. Just a
friendly reminder that over-engineering is something to look
out for, from someone who is prone to over-engineering himself.
Ultimately it is just syntax, it does nothing over what D already
does. It doesn't create anything new. In some cases it
simplifies. If it does, then great, if it doesn't then don't use
it. While I would prefer a totally different syntax, I also like
to keep things organized. Having multiple classes floating around
for certain things is just not needed so there should be an
option.
Re: Rebind template(bug?)
On 08/22/2016 08:04 PM, Engine Machine wrote:
How do you seriously think this is cleaner/simpler? You have two
classes. Their is no uniformity between them. You have uniformity
between all the derived classes then have a special case for the base
class. A certain easy to follow pattern is set up but needlessly break
it for one case. Why?
It avoids the relatively obscure (and badly named, by me)
InstantiateOrEmptySeq template.
You can take this further with template constraints. Gives it a more
uniform appearance at the price of some repetition:
class T()
{
int x;
}
class T(A...) : T!(A[0..$-1])
if (A.length > 0 && A[$-1] == "Animal")
{
int y;
}
class T(A...) : T!(A[0..$-1])
if (A.length > 0 && A[$-1] == "Dog")
{
int z;
}
class T(A...) : T!(A[0..$-1])
if (A.length > 0 && A[$-1] == "Pug")
{
int s;
}
I wouldn't say that this is obviously, objectively, significantly better
than the version with the helper template, though.
By the way, it's not obvious to me what this whole thing achieves in
practice. And whatever benefit there is, it has to be weighed against
the cost of the added complexity.
I don't mean to say that this is not worth pursuing. Just a friendly
reminder that over-engineering is something to look out for, from
someone who is prone to over-engineering himself.
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 07:54:36 UTC, Jack Applegame wrote:
On Monday, 22 August 2016 at 00:43:00 UTC, Engine Machine wrote:
The following code works and does what I want!
template InstantiateOrEmptySeq(alias tmpl, args...)
{
alias Seq(T...)=T;
static if (args.length > 0)
alias InstantiateOrEmptySeq = tmpl!(args[0 .. $-1]);
else
alias InstantiateOrEmptySeq = Seq!();
}
class T(A...) : InstantiateOrEmptySeq!(T, A)
{
static if (A.length == 0)
{
// Base class
int x;
} else
static if (A[$-1] == "Animal")
{
int y;
} else
static if (A[$-1] == "Dog")
{
int z;
} else
static if (A[$-1] == "Pug")
{
int s;
} else static assert(A[$-1]~" not a defined class of
"~this.stringof);
}
Why don't you like a cleaner (in my opinion) solution?
class T() {
// Base class
int x;
}
class T(A...) : T!(A[0..$-1]) {
static if (A[$-1] == "Animal")
{
int y;
} else
static if (A[$-1] == "Dog")
{
int z;
} else
static if (A[$-1] == "Pug")
{
int s;
} else static assert(A[$-1]~" not a defined class of
"~this.stringof);
}
How do you seriously think this is cleaner/simpler? You have two
classes. Their is no uniformity between them. You have uniformity
between all the derived classes then have a special case for the
base class. A certain easy to follow pattern is set up but
needlessly break it for one case. Why?
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 00:43:00 UTC, Engine Machine wrote:
The following code works and does what I want!
template InstantiateOrEmptySeq(alias tmpl, args...)
{
alias Seq(T...)=T;
static if (args.length > 0)
alias InstantiateOrEmptySeq = tmpl!(args[0 .. $-1]);
else
alias InstantiateOrEmptySeq = Seq!();
}
class T(A...) : InstantiateOrEmptySeq!(T, A)
{
static if (A.length == 0)
{
// Base class
int x;
} else
static if (A[$-1] == "Animal")
{
int y;
} else
static if (A[$-1] == "Dog")
{
int z;
} else
static if (A[$-1] == "Pug")
{
int s;
} else static assert(A[$-1]~" not a defined class of
"~this.stringof);
}
Why don't you like a cleaner (in my opinion) solution?
class T() {
// Base class
int x;
}
class T(A...) : T!(A[0..$-1]) {
static if (A[$-1] == "Animal")
{
int y;
} else
static if (A[$-1] == "Dog")
{
int z;
} else
static if (A[$-1] == "Pug")
{
int s;
} else static assert(A[$-1]~" not a defined class of
"~this.stringof);
}
Re: Rebind template(bug?)
On Monday, 22 August 2016 at 00:22:48 UTC, ag0aep6g wrote:
On 08/22/2016 12:06 AM, Engine Machine wrote:
T!()'s "data" is specified in the class just like all the other
derivations. I don't want to have to specify an external base
class as
in your InstaniateOrBase. Why? Because!!! (There should be no
need to,
and if one goes this route of creating classes, it should be
all or
nothing, else there is no real benefit)
You make it sound like I came up with the external base class,
but I just took that from your code.
No, what I meant was I don't want a base. I only added it in my
code so it would compile/do what I want.
[...]
It seems that when one uses `class T(A...) : X`, one can't,
for some X,
not have inheritance. The compiler expects X to be something
inheritable
from no matter what.
I didn't know it, but your code shows that X can also be an
empty compile time list (Seq). I have no idea if this is in the
spec, or if it just happens to work with dmd.
If it's valid D, you just need a template that goes from T and
A to T!(A[0 .. $ - 1]), or if A is already empty, to the empty
Seq.
Like so:
template InstantiateOrEmptySeq(alias tmpl, args...)
{
alias Seq(T...)=T;
static if (args.length > 0)
alias InstantiateOrEmptySeq = tmpl!(args[0 .. $ - 1]);
else
alias InstantiateOrEmptySeq = Seq!();
}
class T(A...) : InstantiateOrEmptySeq!(T, A)
{
...
}
Yes! I though I tried that from Timon's original solution.
The following code works and does what I want!
template InstantiateOrEmptySeq(alias tmpl, args...)
{
alias Seq(T...)=T;
static if (args.length > 0)
alias InstantiateOrEmptySeq = tmpl!(args[0 .. $-1]);
else
alias InstantiateOrEmptySeq = Seq!();
}
class T(A...) : InstantiateOrEmptySeq!(T, A)
{
static if (A.length == 0)
{
// Base class
int x;
} else
static if (A[$-1] == "Animal")
{
int y;
} else
static if (A[$-1] == "Dog")
{
int z;
} else
static if (A[$-1] == "Pug")
{
int s;
} else static assert(A[$-1]~" not a defined class of
"~this.stringof);
}
The only down side is that the static if's are flat. They don't
show the relationship between, say, Dog an Animal, that a nested
set of static if's would show, but I think this is not possible
due to the recursion and shadowing(I imagine one could test if
the variables exist but that is messy).
Anyways, Thanks for the help.
I think this is just Timons answer anyways. What the original
confusion was, was the shadowing, which I thought would not
happen(or at least expected an error), Lodovico solved that.
Re: Rebind template(bug?)
On 08/22/2016 12:06 AM, Engine Machine wrote:
T!()'s "data" is specified in the class just like all the other
derivations. I don't want to have to specify an external base class as
in your InstaniateOrBase. Why? Because!!! (There should be no need to,
and if one goes this route of creating classes, it should be all or
nothing, else there is no real benefit)
You make it sound like I came up with the external base class, but I
just took that from your code.
[...]
It seems that when one uses `class T(A...) : X`, one can't, for some X,
not have inheritance. The compiler expects X to be something inheritable
from no matter what.
I didn't know it, but your code shows that X can also be an empty
compile time list (Seq). I have no idea if this is in the spec, or if it
just happens to work with dmd.
If it's valid D, you just need a template that goes from T and A to
T!(A[0 .. $ - 1]), or if A is already empty, to the empty Seq.
Like so:
template InstantiateOrEmptySeq(alias tmpl, args...)
{
alias Seq(T...)=T;
static if (args.length > 0)
alias InstantiateOrEmptySeq = tmpl!(args[0 .. $ - 1]);
else
alias InstantiateOrEmptySeq = Seq!();
}
class T(A...) : InstantiateOrEmptySeq!(T, A)
{
...
}
Re: Rebind template(bug?)
On Sunday, 21 August 2016 at 21:11:37 UTC, ag0aep6g wrote:
On 08/21/2016 09:29 PM, Engine Machine wrote:
I know you like to play the right or wrong game, but did you
ever learn
that a single example does not prove the truth of something?
But you can show in a single example that something doesn't
work. You tried to do that, and you did it with a simple
example, which is always appreciated. But apparently, you were
wrong. Happens to the best. And when the compiler prints
"tmpl!a" that's indeed a little misleading.
You being wrong there doesn't mean that the Rebind template as
I posted it works correctly, of course. But Jack didn't claim
that. He just said that your example for how it doesn't work is
wrong. And as far as I see, Rebind does work as expected. But I
wouldn't be surprised if there is some edge case where things
fall apart.
Also, if you're looking for help or civil discussion, I suggest
you try a less antagonistic approach. Things like "I know you
like to [play games]" and "did you ever learn [whatever]" do
not set the tone for that.
How about something more complex?
import std.stdio;
import std.meta, std.traits;
class base { }
Style nitpick: Class names in PascalCase, please.
template Rebind(alias instance, newArgs...)
{
import std.traits: TemplateOf;
alias tmpl = TemplateOf!instance;
static if (newArgs.length > 0)
alias Rebind = tmpl!newArgs;
else
alias Rebind = base;
}
template EraseLast(A...)
{
static if (A.length > 0)
alias EraseLast = Erase!(A[$-1], A);
This line can be simplified: alias EraseLast = A[0 .. $ - 1];
else
alias EraseLast = base;
This is quite surprising for a template that's called
"EraseLast". I renamed it to "EraseLastOrBase" for myself when
looking at this.
}
class T(A...) : Rebind!(T!A, EraseLast!A)
The core idea of Rebind isn't needed here, is it? You've got T,
so you can just pass it directly. No need to extract it from
T!A.
So, instead of using some form of Rebind, you can use a simpler
template:
/* Instantiates tmpl with args, or if no args given, returns
base. */
template InstantiateOrBase(alias tmpl, args ...)
{
static if (args.length == 0) alias InstantiateOrBase = base;
else alias InstantiateOrBase = tmpl!args;
}
class T(A...) : InstantiateOrBase!(T, EraseLast!A)
{
int x;
Note that this means that every instantiation of T brings its
own x. That is, T!foo declares an x, and T!(foo, bar) which
inherits from T!foo adds another x. The same happens with y, z,
and s, of course.
static if (A.length > 0 && A[0] == "Animal")
{
int y;
static if (A.length > 1 && A[1] == "Dog")
{
int z;
static if (A.length > 2 && A[2] == "Pug")
int s;
}
}
}
pragma(msg, is(T!("Animal", "Dog", "Pug") : T!("Animal",
"Dog")));
pragma(msg, is(T!("Animal", "Dog", "Pug") : T!("Animal")));
pragma(msg, is(T!("Animal", "Dog", "Pug") : base));
pragma(msg, is(T!("Animal", "Dog") : T!("Animal")));
pragma(msg, is(T!("Animal", "Dog") : base));
pragma(msg, is(T!("Animal") : base));
Asserts are great to show that something holds. When someone
like me makes changes to your code in order to understand it,
the complier throws a nice loud error in their face when they
mess up. So I changed these to static asserts for myself.
// all true
void main()
{
auto t = new T!("Animal", "Dog", "Pug")();
T!("Animal", "Dog") q = t;
//T!("Animal", "Dog", "Pug") q = t; works but then q
is not the
super of t
t.x = 3;
t.y = 4;
t.z = 6;
t.s = 123;
q.y = 1;
writeln(t, ", ", typeof(t).stringof);
writeln(q, ", ", typeof(q).stringof);
writeln("---");
writeln(t.x);
writeln(t.y);
writeln(t.z);
writeln(t.s);
writeln("---");
writeln(q.x);
writeln(q.y);
writeln(q.z);
writeln("---");
writeln(t.y);
writeln("---");
writeln(&t);
writeln(&q);
}
Since the pragma's are true, it is obvious that the
inheritance should
work chain works. Yet q is not a reference to t as it should
be, why is
this?
It would help a lot if you would point out what parts of the
output are surprising to you. If you let the reader figure it
out themselves, chances are 1) people are not going to bother,
and 2) if they do bother, they might miss your point.
Labeling the output also helps. By that I mean, if you writ
Re: Rebind template(bug?)
On 08/21/2016 09:29 PM, Engine Machine wrote:
I know you like to play the right or wrong game, but did you ever learn
that a single example does not prove the truth of something?
But you can show in a single example that something doesn't work. You
tried to do that, and you did it with a simple example, which is always
appreciated. But apparently, you were wrong. Happens to the best. And
when the compiler prints "tmpl!a" that's indeed a little misleading.
You being wrong there doesn't mean that the Rebind template as I posted
it works correctly, of course. But Jack didn't claim that. He just said
that your example for how it doesn't work is wrong. And as far as I see,
Rebind does work as expected. But I wouldn't be surprised if there is
some edge case where things fall apart.
Also, if you're looking for help or civil discussion, I suggest you try
a less antagonistic approach. Things like "I know you like to [play
games]" and "did you ever learn [whatever]" do not set the tone for that.
How about something more complex?
import std.stdio;
import std.meta, std.traits;
class base { }
Style nitpick: Class names in PascalCase, please.
template Rebind(alias instance, newArgs...)
{
import std.traits: TemplateOf;
alias tmpl = TemplateOf!instance;
static if (newArgs.length > 0)
alias Rebind = tmpl!newArgs;
else
alias Rebind = base;
}
template EraseLast(A...)
{
static if (A.length > 0)
alias EraseLast = Erase!(A[$-1], A);
This line can be simplified: alias EraseLast = A[0 .. $ - 1];
else
alias EraseLast = base;
This is quite surprising for a template that's called "EraseLast". I
renamed it to "EraseLastOrBase" for myself when looking at this.
}
class T(A...) : Rebind!(T!A, EraseLast!A)
The core idea of Rebind isn't needed here, is it? You've got T, so you
can just pass it directly. No need to extract it from T!A.
So, instead of using some form of Rebind, you can use a simpler template:
/* Instantiates tmpl with args, or if no args given, returns base. */
template InstantiateOrBase(alias tmpl, args ...)
{
static if (args.length == 0) alias InstantiateOrBase = base;
else alias InstantiateOrBase = tmpl!args;
}
class T(A...) : InstantiateOrBase!(T, EraseLast!A)
{
int x;
Note that this means that every instantiation of T brings its own x.
That is, T!foo declares an x, and T!(foo, bar) which inherits from T!foo
adds another x. The same happens with y, z, and s, of course.
static if (A.length > 0 && A[0] == "Animal")
{
int y;
static if (A.length > 1 && A[1] == "Dog")
{
int z;
static if (A.length > 2 && A[2] == "Pug")
int s;
}
}
}
pragma(msg, is(T!("Animal", "Dog", "Pug") : T!("Animal", "Dog")));
pragma(msg, is(T!("Animal", "Dog", "Pug") : T!("Animal")));
pragma(msg, is(T!("Animal", "Dog", "Pug") : base));
pragma(msg, is(T!("Animal", "Dog") : T!("Animal")));
pragma(msg, is(T!("Animal", "Dog") : base));
pragma(msg, is(T!("Animal") : base));
Asserts are great to show that something holds. When someone like me
makes changes to your code in order to understand it, the complier
throws a nice loud error in their face when they mess up. So I changed
these to static asserts for myself.
// all true
void main()
{
auto t = new T!("Animal", "Dog", "Pug")();
T!("Animal", "Dog") q = t;
//T!("Animal", "Dog", "Pug") q = t; works but then q is not the
super of t
t.x = 3;
t.y = 4;
t.z = 6;
t.s = 123;
q.y = 1;
writeln(t, ", ", typeof(t).stringof);
writeln(q, ", ", typeof(q).stringof);
writeln("---");
writeln(t.x);
writeln(t.y);
writeln(t.z);
writeln(t.s);
writeln("---");
writeln(q.x);
writeln(q.y);
writeln(q.z);
writeln("---");
writeln(t.y);
writeln("---");
writeln(&t);
writeln(&q);
}
Since the pragma's are true, it is obvious that the inheritance should
work chain works. Yet q is not a reference to t as it should be, why is
this?
It would help a lot if you would point out what parts of the output are
surprising to you. If you let the reader figure it out themselves,
chances are 1) people are not going to bother, and 2) if they do bother,
they might miss your point.
Labeling the output also helps. By that I mean, if you write
`writeln("t.x: ", t.x);`, the output can be read much more easily. I
al
Re: Rebind template(bug?)
On Sunday, 21 August 2016 at 20:36:54 UTC, Engine Machine wrote: On Sunday, 21 August 2016 at 19:42:08 UTC, Lodovico Giaretta wrote: [...] You're right. I didn't realize that variables could be shadowed in classes. Seems dangerous. D doesn't allow shadowing in a normal context and gives an error so I don't know why it wouldn't do that in classes. (since it wasn't giving an error I thought it wasn't shadowing) You are right. It is very bad. But as far as I know Java and C++ allow this too. I will open an enhancement request (if there's none about this), to gather some feedback on the matter.
Re: Rebind template(bug?)
On Sunday, 21 August 2016 at 19:42:08 UTC, Lodovico Giaretta
wrote:
On Sunday, 21 August 2016 at 19:29:26 UTC, Engine Machine wrote:
[...]
The problem of this code has nothing to do with aliases. They
work correctly. The problem is variable shadowing. In the
following code, Child has two x variables, one of which is only
accessible from a Parent reference, the other only from a Child
reference.
class Parent
{
int x;
}
class Child: Parent
{
int x; // this shadows Parent.x
int y;
}
void main()
{
Child child = new Child();
Parent parent = child;
child.x = child.y = 3;
parent.x = 2;
assert(child.x == 3);
assert((cast(Child)parent).x == 3);
assert((cast(Parent)child).x == 2);
assert(parent is child); // same object (remember that a
class is already a pointer);
assert(&parent != &child); // but there are two different
pointers on the stack (pointing to the same object)
}
You're right. I didn't realize that variables could be shadowed
in classes. Seems dangerous. D doesn't allow shadowing in a
normal context and gives an error so I don't know why it wouldn't
do that in classes. (since it wasn't giving an error I thought it
wasn't shadowing)
Re: Rebind template(bug?)
On Sunday, 21 August 2016 at 19:29:26 UTC, Engine Machine wrote: I know you like to play the right or wrong game, but did you ever learn that a single example does not prove the truth of something? How about something more complex? Your demagogy will not help you learn the basics of the D language. And you're wrong again, young arrogant padawan.
Re: Rebind template
On Saturday, 20 August 2016 at 22:18:57 UTC, Engine Machine wrote:
On Saturday, 20 August 2016 at 22:11:40 UTC, Engine Machine
wrote:
Is there a way to rebind the arguments of a template?
template foo(X)
{
// X is like A!(a,b,c)
Y = Rebind!(X,d,e,f);
// Y is like A!(d,e,f);
}
foo(A!(a,b,c));
?
I'd also be happy if I could just remove the last element from
A.
template EraseLast(X)
{
// returns A!(a,b) when X = A!(a,b,c)
}
Check for ApplyLeft and ApplyRight in std.meta, maybe it can help
you.
http://dlang.org/phobos/std_meta.html#.ApplyLeft
http://dlang.org/phobos/std_meta.html#.ApplyRight
Re: Rebind template(bug?)
On Sunday, 21 August 2016 at 19:42:08 UTC, Lodovico Giaretta
wrote:
On Sunday, 21 August 2016 at 19:29:26 UTC, Engine Machine wrote:
[...]
The problem of this code has nothing to do with aliases. They
work correctly. The problem is variable shadowing. In the
following code, Child has two x variables, one of which is only
accessible from a Parent reference, the other only from a Child
reference.
class Parent
{
int x;
}
class Child: Parent
{
int x; // this shadows Parent.x
int y;
}
void main()
{
Child child = new Child();
Parent parent = child;
child.x = child.y = 3;
parent.x = 2;
assert(child.x == 3);
assert((cast(Child)parent).x == 3);
assert((cast(Parent)child).x == 2);
assert(parent is child); // same object (remember that a
class is already a pointer);
assert(&parent != &child); // but there are two different
pointers on the stack (pointing to the same object)
}
A patch to your code that makes it work, with the parts not
displayed unchanged:
class base
{
int x;
}
class T(A...) : Rebind!(T!A, EraseLast!A)
{
static if(A[$-1] == "Animal")
int y;
else static if (A[$-1] == "Dog")
int z;
else static if (A[$-1] == "Pug")
int s;
}
Re: Rebind template(bug?)
On Sunday, 21 August 2016 at 19:29:26 UTC, Engine Machine wrote:
[...]
The problem of this code has nothing to do with aliases. They
work correctly. The problem is variable shadowing. In the
following code, Child has two x variables, one of which is only
accessible from a Parent reference, the other only from a Child
reference.
class Parent
{
int x;
}
class Child: Parent
{
int x; // this shadows Parent.x
int y;
}
void main()
{
Child child = new Child();
Parent parent = child;
child.x = child.y = 3;
parent.x = 2;
assert(child.x == 3);
assert((cast(Child)parent).x == 3);
assert((cast(Parent)child).x == 2);
assert(parent is child); // same object (remember that a
class is already a pointer);
assert(&parent != &child); // but there are two different
pointers on the stack (pointing to the same object)
}
Re: Rebind template(bug?)
On Sunday, 21 August 2016 at 06:28:25 UTC, Jack Applegame wrote:
On Sunday, 21 August 2016 at 00:06:07 UTC, Engine Machine wrote:
On Saturday, 20 August 2016 at 22:21:00 UTC, ag0aep6g wrote:
On 08/21/2016 12:11 AM, Engine Machine wrote:
Is there a way to rebind the arguments of a template?
template foo(X)
{
// X is like A!(a,b,c)
Y = Rebind!(X,d,e,f);
// Y is like A!(d,e,f);
}
foo(A!(a,b,c));
?
template Rebind(alias instance, newArgs...)
{
import std.traits: TemplateOf;
alias tmpl = TemplateOf!instance;
alias Rebind = tmpl!newArgs;
}
This doesn't work because the rebound type is of type tmpl and
not the original
e.g.,
Rebind!(T!b, a)
is tmpl!a not T!a.
You are wrong. tmpl is just alias of template T. So tmpl!a and
T!a are the same type.
alias X = T!(int, short, char);
alias Y = Rebind!(X, short, char, int);
static assert(is(Y == T!(short, char, int))); // passes
I know you like to play the right or wrong game, but did you ever
learn that a single example does not prove the truth of something?
How about something more complex?
import std.stdio;
import std.meta, std.traits;
class base { }
template Rebind(alias instance, newArgs...)
{
import std.traits: TemplateOf;
alias tmpl = TemplateOf!instance;
static if (newArgs.length > 0)
alias Rebind = tmpl!newArgs;
else
alias Rebind = base;
}
template EraseLast(A...)
{
static if (A.length > 0)
alias EraseLast = Erase!(A[$-1], A);
else
alias EraseLast = base;
}
class T(A...) : Rebind!(T!A, EraseLast!A)
{
int x;
static if (A.length > 0 && A[0] == "Animal")
{
int y;
static if (A.length > 1 && A[1] == "Dog")
{
int z;
static if (A.length > 2 && A[2] == "Pug")
int s;
}
}
}
pragma(msg, is(T!("Animal", "Dog", "Pug") : T!("Animal", "Dog")));
pragma(msg, is(T!("Animal", "Dog", "Pug") : T!("Animal")));
pragma(msg, is(T!("Animal", "Dog", "Pug") : base));
pragma(msg, is(T!("Animal", "Dog") : T!("Animal")));
pragma(msg, is(T!("Animal", "Dog") : base));
pragma(msg, is(T!("Animal") : base));
// all true
void main()
{
auto t = new T!("Animal", "Dog", "Pug")();
T!("Animal", "Dog") q = t;
//T!("Animal", "Dog", "Pug") q = t; works but then q is
not the super of t
t.x = 3;
t.y = 4;
t.z = 6;
t.s = 123;
q.y = 1;
writeln(t, ", ", typeof(t).stringof);
writeln(q, ", ", typeof(q).stringof);
writeln("---");
writeln(t.x);
writeln(t.y);
writeln(t.z);
writeln(t.s);
writeln("---");
writeln(q.x);
writeln(q.y);
writeln(q.z);
writeln("---");
writeln(t.y);
writeln("---");
writeln(&t);
writeln(&q);
}
Since the pragma's are true, it is obvious that the inheritance
should work chain works. Yet q is not a reference to t as it
should be, why is this? If aliases were truly aliases as you
think(your generic response) then it should work because rebind
and erase only use aliases.
Re: Rebind template
On Sunday, 21 August 2016 at 00:06:07 UTC, Engine Machine wrote:
On Saturday, 20 August 2016 at 22:21:00 UTC, ag0aep6g wrote:
On 08/21/2016 12:11 AM, Engine Machine wrote:
Is there a way to rebind the arguments of a template?
template foo(X)
{
// X is like A!(a,b,c)
Y = Rebind!(X,d,e,f);
// Y is like A!(d,e,f);
}
foo(A!(a,b,c));
?
template Rebind(alias instance, newArgs...)
{
import std.traits: TemplateOf;
alias tmpl = TemplateOf!instance;
alias Rebind = tmpl!newArgs;
}
This doesn't work because the rebound type is of type tmpl and
not the original
e.g.,
Rebind!(T!b, a)
is tmpl!a not T!a.
You are wrong. tmpl is just alias of template T. So tmpl!a and
T!a are the same type.
alias X = T!(int, short, char);
alias Y = Rebind!(X, short, char, int);
static assert(is(Y == T!(short, char, int))); // passes
Re: Rebind template
On Saturday, 20 August 2016 at 22:21:00 UTC, ag0aep6g wrote:
On 08/21/2016 12:11 AM, Engine Machine wrote:
Is there a way to rebind the arguments of a template?
template foo(X)
{
// X is like A!(a,b,c)
Y = Rebind!(X,d,e,f);
// Y is like A!(d,e,f);
}
foo(A!(a,b,c));
?
template Rebind(alias instance, newArgs...)
{
import std.traits: TemplateOf;
alias tmpl = TemplateOf!instance;
alias Rebind = tmpl!newArgs;
}
This doesn't work because the rebound type is of type tmpl and
not the original
e.g.,
Rebind!(T!b, a)
is tmpl!a not T!a.
Re: Rebind template
On 08/21/2016 12:11 AM, Engine Machine wrote:
Is there a way to rebind the arguments of a template?
template foo(X)
{
// X is like A!(a,b,c)
Y = Rebind!(X,d,e,f);
// Y is like A!(d,e,f);
}
foo(A!(a,b,c));
?
template Rebind(alias instance, newArgs...)
{
import std.traits: TemplateOf;
alias tmpl = TemplateOf!instance;
alias Rebind = tmpl!newArgs;
}
Re: Rebind template
On Saturday, 20 August 2016 at 22:11:40 UTC, Engine Machine wrote:
Is there a way to rebind the arguments of a template?
template foo(X)
{
// X is like A!(a,b,c)
Y = Rebind!(X,d,e,f);
// Y is like A!(d,e,f);
}
foo(A!(a,b,c));
?
I'd also be happy if I could just remove the last element from A.
template EraseLast(X)
{
// returns A!(a,b) when X = A!(a,b,c)
}
Rebind template
Is there a way to rebind the arguments of a template?
template foo(X)
{
// X is like A!(a,b,c)
Y = Rebind!(X,d,e,f);
// Y is like A!(d,e,f);
}
foo(A!(a,b,c));
?
