Re: to compose or hack?
On Wednesday, 7 July 2021 at 01:44:20 UTC, Steven Schveighoffer
wrote:
But it got me thinking, how often do people roll their own vs.
trying to compose using existing Phobos nuggets?
When there's not an obvious/simple way to do something by
composing ranges, I tend to just give up and write procedural
code instead. Yes, the resulting code is longer and more prone to
logic bugs, but there's no limit to what you can do and it's
easier to see what's going on at a lower level. I also don't tend
to let composed ranges leave the function they were created in, I
rather pass simple arrays around than complex objects depending
on multiple inputs from different sources.
I don't know what the destination of your range is so this might
not be applicable, but I'd probably end up writing a function
with an OutputRange like this:
```D
void putRangeInterleaved(O, R, E)(ref O sink, R range, E
separator) {
import std.range.primitives: put;
if (!range.empty) {
put(sink, range.front);
range.popFront();
}
foreach(ref elem; range) {
put(sink, separator);
put(sink, elem);
}
}
```
I'm not trying to discourage anyone from writing range code, I'm
just presenting this as an alternative in case it's useful.
Re: to compose or hack?
On 7/7/21 3:52 PM, Sebastiaan Koppe wrote:
On Wednesday, 7 July 2021 at 13:30:28 UTC, Steven Schveighoffer wrote:
On 7/7/21 5:54 AM, rassoc wrote:
On Wednesday, 7 July 2021 at 01:44:20 UTC, Steven Schveighoffer wrote:
So I have this situation where I need to split a string, then where
the splits are, insert a string to go between the elements making a
new range, all without allocating (hopefully).
Without considering the more general case, isn't that just
splitter-joiner?
No, splitter-joiner would make a range of characters, I want a range
of strings.
Just lift each item in a range then:
```d
import std;
auto foo(string s, string sp, string j) @nogc {
return s.splitter(sp).map!(i => only(i)).joiner(only(j));
}
void main() {
foo("ab,cd,ef,gh", ",", "##").writeln; // => ["ab", "##", "cd",
"##", "ef", "##", "gh"]
}
```
Thanks! This is exactly what I was reaching for. `only` is one of the
coolest functions (I use it elsewhere too).
-Steve
Re: to compose or hack?
On Wednesday, 7 July 2021 at 19:52:30 UTC, Sebastiaan Koppe wrote:
Just lift each item in a range then:
```d
import std;
auto foo(string s, string sp, string j) @nogc {
return s.splitter(sp).map!(i => only(i)).joiner(only(j));
}
```
Code golf: `map!(i => only(i))` can be shortened to `map!only`.
Re: to compose or hack?
On Wednesday, 7 July 2021 at 13:30:28 UTC, Steven Schveighoffer
wrote:
On 7/7/21 5:54 AM, rassoc wrote:
On Wednesday, 7 July 2021 at 01:44:20 UTC, Steven
Schveighoffer wrote:
So I have this situation where I need to split a string, then
where the splits are, insert a string to go between the
elements making a new range, all without allocating
(hopefully).
Without considering the more general case, isn't that just
splitter-joiner?
No, splitter-joiner would make a range of characters, I want a
range of strings.
Just lift each item in a range then:
```d
import std;
auto foo(string s, string sp, string j) @nogc {
return s.splitter(sp).map!(i => only(i)).joiner(only(j));
}
void main() {
foo("ab,cd,ef,gh", ",", "##").writeln; // => ["ab", "##",
"cd", "##", "ef", "##", "gh"]
}
```
Re: to compose or hack?
On 7/7/21 5:54 AM, rassoc wrote:
On Wednesday, 7 July 2021 at 01:44:20 UTC, Steven Schveighoffer wrote:
So I have this situation where I need to split a string, then where
the splits are, insert a string to go between the elements making a
new range, all without allocating (hopefully).
Without considering the more general case, isn't that just splitter-joiner?
No, splitter-joiner would make a range of characters, I want a range of
strings.
```d
import std;
auto foo(string s, string sp, string j) @nogc {
return s.splitter(sp).joiner(j);
}
void main() {
foo("ab,cd,ef,gh", ",", "##").writeln; // => ab##cd##ef##gh
}
```
Using your example, the correct result should be `["ab", "##", "cd",
"##", "ef", "##", "gh"]`
Interesting! Tried it myself, shame that this doesn't quite work:
```d
import std;
auto foo(R)(string s, string sp, R r) @nogc {
return s.splitter(sp).zip(r)
.map!(a => a.expand.only)
.joiner.dropBackOne.joiner; // not bidirectional
}
void main() {
foo("ab,cd,ef,gh", ",", ["##", "**"].cycle).writeln;
}
```
ooh, I like the zip/expand/only trick! I got this to work, and lol, I
don't think I'd ever use this:
```d
auto interleave(R, U)(R src, U middles) if (isInputRange!R && is(U ==
ElementType!R))
{
return zip(StoppingPolicy.shortest, src, middles.repeat)
.map!(e => only(e.expand))
.joiner
.slide(2)
.frontTransversal;
}
```
Ironically, I think it would still run the splitting algorithm 2x,
because `slide` has to store 2 copies of the source range. And it's not
nogc either. Hm... I bet `dropBackOne` might actually be able to work on
a forward range if it cached one element? But that might be iffy.
-Steve
Re: to compose or hack?
On 7/6/21 11:42 PM, Jon Degenhardt wrote: On Wednesday, 7 July 2021 at 01:44:20 UTC, Steven Schveighoffer wrote: This is pretty minimal, but does what I want it to do. Is it ready for inclusion in Phobos? Not by a longshot! A truly generic interleave would properly forward everything else that the range supports (like `length`, `save`, etc). But it got me thinking, how often do people roll their own vs. trying to compose using existing Phobos nuggets? I found this pretty satisfying, even if I didn't test it to death and maybe I use it only in one place. Do you find it difficult to use Phobos in a lot of situations to compose your specialized ranges? I try to compose using existing Phobos facilities, but don't hesitate to write my own ranges. The reasons are usually along the lines you describe. For one, range creation is easy in D, consistent with the pro/con tradeoffs described in the thread/talk [Iterator and Ranges: Comparing C++ to D to Rust](https://forum.dlang.org/thread/diexjstekiyzgxlic...@forum.dlang.org). Another is that if application/task specific logic is involved, it is often simpler/faster to just incorporate it into the range rather than figure out how to factor it out of the more general range. Especially if the range is not going to be used much. Yeah, I agree with all this. I do try to use existing ranges/algorithms as much as possible. But I find it awesome you can just whip up a quick shim range to get work done and not worry about making it perfect for general consumption. Kind of like a lambda range ;) -Steve
Re: to compose or hack?
On Wednesday, 7 July 2021 at 01:44:20 UTC, Steven Schveighoffer
wrote:
So I have this situation where I need to split a string, then
where the splits are, insert a string to go between the
elements making a new range, all without allocating (hopefully).
Without considering the more general case, isn't that just
splitter-joiner?
```d
import std;
auto foo(string s, string sp, string j) @nogc {
return s.splitter(sp).joiner(j);
}
void main() {
foo("ab,cd,ef,gh", ",", "##").writeln; // => ab##cd##ef##gh
}
```
Looking around phobos I found inside the documentation of
[roundRobin](https://dlang.org/phobos/std_range.html#.roundRobin) something that does *exactly* what I'm looking for.
Except... the provided `interleave` function iterates the
original range twice, which means 2x the searching calls for
splitter. Why does it do this? Because `roundRobin` will keep
going as long as ANY range still has data left, so you need to
make the "interleaving" range stop when the first one stops.
Interesting! Tried it myself, shame that this doesn't quite work:
```d
import std;
auto foo(R)(string s, string sp, R r) @nogc {
return s.splitter(sp).zip(r)
.map!(a => a.expand.only)
.joiner.dropBackOne.joiner; // not bidirectional
}
void main() {
foo("ab,cd,ef,gh", ",", ["##", "**"].cycle).writeln;
}
```
Re: to compose or hack?
On Wednesday, 7 July 2021 at 01:44:20 UTC, Steven Schveighoffer wrote: This is pretty minimal, but does what I want it to do. Is it ready for inclusion in Phobos? Not by a longshot! A truly generic interleave would properly forward everything else that the range supports (like `length`, `save`, etc). But it got me thinking, how often do people roll their own vs. trying to compose using existing Phobos nuggets? I found this pretty satisfying, even if I didn't test it to death and maybe I use it only in one place. Do you find it difficult to use Phobos in a lot of situations to compose your specialized ranges? I try to compose using existing Phobos facilities, but don't hesitate to write my own ranges. The reasons are usually along the lines you describe. For one, range creation is easy in D, consistent with the pro/con tradeoffs described in the thread/talk [Iterator and Ranges: Comparing C++ to D to Rust](https://forum.dlang.org/thread/diexjstekiyzgxlic...@forum.dlang.org). Another is that if application/task specific logic is involved, it is often simpler/faster to just incorporate it into the range rather than figure out how to factor it out of the more general range. Especially if the range is not going to be used much. --Jon
to compose or hack?
So I have this situation where I need to split a string, then where the
splits are, insert a string to go between the elements making a new
range, all without allocating (hopefully).
Looking around phobos I found inside the documentation of
[roundRobin](https://dlang.org/phobos/std_range.html#.roundRobin)
something that does *exactly* what I'm looking for.
Except... the provided `interleave` function iterates the original range
twice, which means 2x the searching calls for splitter. Why does it do
this? Because `roundRobin` will keep going as long as ANY range still
has data left, so you need to make the "interleaving" range stop when
the first one stops.
After struggling to think up ways to compose this (hm.., can I make the
ranges share a stopping point?) without the 2x penalty, I just decided
to write my own interleave range which does exactly what I am looking for:
```d
auto interleave(R, U)(R src, U middles) if (isInputRange!R && is(U ==
ElementType!R))
{
static struct Result
{
R src;
U middles;
bool between = false;
auto front() {
assert(!empty);
return between ? middles : src.front;
}
void popFront() {
assert(!empty);
if(between)
between = false;
else
{
src.popFront;
between = true;
}
}
bool empty()
{
return src.empty;
}
}
return Result(src, middles);
}
```
This is pretty minimal, but does what I want it to do. Is it ready for
inclusion in Phobos? Not by a longshot! A truly generic interleave would
properly forward everything else that the range supports (like `length`,
`save`, etc).
But it got me thinking, how often do people roll their own vs. trying to
compose using existing Phobos nuggets? I found this pretty satisfying,
even if I didn't test it to death and maybe I use it only in one place.
Do you find it difficult to use Phobos in a lot of situations to compose
your specialized ranges?
Oh, and if you do know of a better way to compose the range that doesn't
require the double iteration, I'd be interested in seeing it.
-Steve
