I kept in my head what Matthew said about implementing a for_each. I thought this couldn't be so hard, so I checked how it works in STL (since I don't know STL), and I wrote this:

template ForEach(InputIter) {
    alias void delegate (InputIter) Function;
    Function foreach(InputIter first,InputIter last,Function f) {
        for ( ; first!=last ; first++)
            f(first);
        return f;
    }
}

and if I try it with:

void f(int x) {
    printf("%d\n",x);
}
instance ForEach(int) Ints;
Ints.foreach(4,10,f);

It works just fine. Now the problem.

I decided I should test it also with something else, something like a node in a linked list. For a very simple node, I implemented the postinc() operator, but it just doesn't seem to work.

class Node {
    Node next;
    float x;
    this(float a) { x=a;}
    Node postinc() {
        // what goes here??
    }
}

I tried all the following:
1) return next;
2) this=next; return this;
3) this=next; return next;
4) Node tmp=next; this=next; return tmp;
5) return new Node(next.x);

But nothing seems to work. Most likely I have the wrong idea of what I have to do, but I believe you guys understand what I want to accomplish.

-------------------------
Carlos Santander


---
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> I kept in my head what Matthew said

The first step on the road to ruin ...

> about implementing a for_each. I thought
> this couldn't be so hard, so I checked how it works in STL (since I don't
> know STL), and I wrote this:
>
> template ForEach(InputIter) {
>     alias void delegate (InputIter) Function;
>     Function foreach(InputIter first,InputIter last,Function f) {
>         for ( ; first!=last ; first++)
>             f(first);
>         return f;
>     }
> }
>
> and if I try it with:
>
> void f(int x) {
>     printf("%d\n",x);
> }
> instance ForEach(int) Ints;
> Ints.foreach(4,10,f);
>
> It works just fine. Now the problem.
>
> I decided I should test it also with something else, something like a node in a linked list. For a very simple node, I implemented the postinc() operator, but it just doesn't seem to work.
>
> class Node {
>     Node next;
>     float x;
>     this(float a) { x=a;}
>     Node postinc() {
>         // what goes here??
>     }
> }
>
> I tried all the following:
> 1) return next;
> 2) this=next; return this;
> 3) this=next; return next;
> 4) Node tmp=next; this=next; return tmp;
> 5) return new Node(next.x);
>
> But nothing seems to work. Most likely I have the wrong idea of what I
have
> to do, but I believe you guys understand what I want to accomplish.

I know what you want to do, but I have no idea.

I want to see an implementation of for_each() that works for two sequence types - say a built in array of double and a template-list of Thing objects (Thing is any UDT) - and with two completely different functors - say a stateful one that sums the .size of each element and a stateless one that dumps them to stdout.

No offence to anyone on the NG - and *please* correct me if I'm wrong - but I expect Walter's the only one who currently could do this if it's possible, which I strongly suspect it is not.

On both issues I'm dying to be wrong - partly because I simply want to learn how this is done - but until I am we can't say we're even in a position to ask the right questions about a DTL, never mind answer them

Yours seeking enlightenment


-- 
Matthew Wilson

STLSoft moderator and C++ monomaniac

mailto:matthew@stlsoft.org
http://www.stlsoft.org
news://news.digitalmars.com/c++.stlsoft

"I can't sleep nights till I found out who hurled what ball through what apparatus" -- Dr Niles Crane

----------------------------------------------------------------------------
---

"Matthew Wilson" <matthew@stlsoft.org> wrote in message
news:bgvh60$205c$1@digitaldaemon.com...
| > I kept in my head what Matthew said
|
| The first step on the road to ruin ...
|

I certainly don't think so...

| >
| > But nothing seems to work. Most likely I have the wrong idea of what I
| have
| > to do, but I believe you guys understand what I want to accomplish.
|
| I know what you want to do, but I have no idea.
|
| I want to see an implementation of for_each() that works for two sequence
| types - say a built in array of double and a template-list of Thing
objects
| (Thing is any UDT) - and with two completely different functors - say a
| stateful one that sums the .size of each element and a stateless one that
| dumps them to stdout.
|

I'm not so sure if you understand. What I wanted was that by applying postinc() to  a Node, it could move to the next one.

————————————————————————— Carlos Santander



---
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Checked by AVG anti-virus system (http://www.grisoft.com).
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"Carlos Santander B." <carlos8294@msn.com> wrote in message news:bh0vuj$bnh$1@digitaldaemon.com...
> "Matthew Wilson" <matthew@stlsoft.org> wrote in message
> news:bgvh60$205c$1@digitaldaemon.com...
> | > I kept in my head what Matthew said
> |
> | The first step on the road to ruin ...
> |
>
> I certainly don't think so...

Who is the bigger fool, the fool himself or the fool who follows him.

> | >
> | > But nothing seems to work. Most likely I have the wrong idea of what I
> | have
> | > to do, but I believe you guys understand what I want to accomplish.
> |
> | I know what you want to do, but I have no idea.
> |
> | I want to see an implementation of for_each() that works for two
sequence
> | types - say a built in array of double and a template-list of Thing
> objects
> | (Thing is any UDT) - and with two completely different functors - say a
> | stateful one that sums the .size of each element and a stateless one
that
> | dumps them to stdout.
> |
>
> I'm not so sure if you understand. What I wanted was that by applying postinc() to  a Node, it could move to the next one.

I did understand what you were saying. I was playing "development manager" by countering your need with a completely different and much broader requirement. ;)

I want Walter to do this, I think, as it will save all us poor D-lovers-but-somewhat-lacking-in-groking-the-templates many hours of brain ache.

Walter. Walter!! WALTER. _please_ help us, grovel groval

:)

Dr Proctor and the early morning gremlins.

"Matthew Wilson" <matthew@stlsoft.org> wrote in news:bgvh60$205c$1@digitaldaemon.com:

> I want to see an implementation of for_each() that works for two sequence types - say a built in array of double and a template-list of Thing objects (Thing is any UDT) - and with two completely different functors - say a stateful one that sums the .size of each element and a stateless one that dumps them to stdout.
> 
> No offence to anyone on the NG - and *please* correct me if I'm wrong - but I expect Walter's the only one who currently could do this if it's possible, which I strongly suspect it is not.

I guess you just want to torture Walter by letting him write templated
stuff. Well, I tought what's worse than writting templated stuff?
Having to read templated stuff, written by someone else, of course. <grin>

See the attachment for one solution of the given task.
Note:
In the example I used the template-list in combination with long[]
build-in arrays, instead of plain build-in arrays of double.


> 
> On both issues I'm dying to be wrong - partly because I simply want to learn how this is done - but until I am we can't say we're even in a position to ask the right questions about a DTL, never mind answer them

Agree.

Just want to acknowledge that I've got this. I've just got a bit "under" with workload, and cannot look at the template stuff now, but I promise to do so in a few weeks.

Hopefully all you good people will have it sorted by then. ;)

"Farmer" <itsFarmer.@freenet.de> wrote in message news:Xns93D3A64045070itsFarmer@63.105.9.61...
> "Matthew Wilson" <matthew@stlsoft.org> wrote in news:bgvh60$205c$1@digitaldaemon.com:
>
> > I want to see an implementation of for_each() that works for two sequence types - say a built in array of double and a template-list of Thing objects (Thing is any UDT) - and with two completely different functors - say a stateful one that sums the .size of each element and a stateless one that dumps them to stdout.
> >
> > No offence to anyone on the NG - and *please* correct me if I'm wrong - but I expect Walter's the only one who currently could do this if it's possible, which I strongly suspect it is not.
>
> I guess you just want to torture Walter by letting him write templated
> stuff. Well, I tought what's worse than writting templated stuff?
> Having to read templated stuff, written by someone else, of course. <grin>
>
> See the attachment for one solution of the given task.
> Note:
> In the example I used the template-list in combination with long[]
> build-in arrays, instead of plain build-in arrays of double.
>
>
> >
> > On both issues I'm dying to be wrong - partly because I simply want to learn how this is done - but until I am we can't say we're even in a position to ask the right questions about a DTL, never mind answer them
>
> Agree.
>
>
>
>
>
>

"Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bh14tp$g9j$1@digitaldaemon.com...
> Walter. Walter!! WALTER. _please_ help us, grovel groval

Would a nice foreach that worked on arrays as easilly as collection classes do the thing?

On Tue, 12 Aug 2003 20:18:00 -0700, Walter wrote:

> 
> "Matthew Wilson" <matthew@stlsoft.org> wrote in message news:bh14tp$g9j$1@digitaldaemon.com...
>> Walter. Walter!! WALTER. _please_ help us, grovel groval
> 
> Would a nice foreach that worked on arrays as easilly as collection classes do the thing?

Yes!!!!