Re: joiner: How to iterate over immutable ranges?
On Monday, 15 February 2016 at 18:13:48 UTC, Ali Çehreli wrote: On 02/15/2016 06:25 AM, Bastiaan Veelo wrote: > I didn't even know about save... Its documentation is hidden > quite > well, because I still cannot find it. Heh. :) It is a part of the ForwardRange interface (more correctly, "concept"?). It looks like "the additional capability that one can save one's current position with the save primitive" under isForwardRange is its official documentation: http://dlang.org/phobos/std_range_primitives.html Wow, thanks. I did search that page before, but that section didn't give an echo on my radar...
Re: joiner: How to iterate over immutable ranges?
On 02/15/2016 06:25 AM, Bastiaan Veelo wrote: > I didn't even know about save... Its documentation is hidden quite > well, because I still cannot find it. Heh. :) It is a part of the ForwardRange interface (more correctly, "concept"?). It looks like "the additional capability that one can save one's current position with the save primitive" under isForwardRange is its official documentation: http://dlang.org/phobos/std_range_primitives.html > Seems it is about time I read the books. Agreed. Ranges is a concept where a little bit of documentation up front makes the ideas very clear. Ali
Re: joiner: How to iterate over immutable ranges?
On Monday, 15 February 2016 at 01:42:30 UTC, Mike Parker wrote: On Sunday, 14 February 2016 at 19:32:31 UTC, Bastiaan Veelo wrote: Maybe this [1] will help shed some light. [1] https://www.packtpub.com/books/content/understanding-ranges Good idea. I have your book, but it is very nice to have this particular chapter freely online. Thanks, Bastiaan.
Re: joiner: How to iterate over immutable ranges?
On Monday, 15 February 2016 at 01:14:10 UTC, Ali Çehreli wrote:
On 02/14/2016 11:32 AM, Bastiaan Veelo wrote:
If it's acceptable for you, the following code calls .save on
the elements and it works:
import std.algorithm.iteration;
import std.stdio;
import std.array;// <-- ADDED
void main()
{
immutable(string[])[] icycles;
icycles ~= ["one", "two"];
icycles ~= ["three", "four"];
foreach (number; icycles.map!(r => r.save).joiner)
writeln(number);
}
Again, .save on an array is cheap. What will happen is that the
original immutable arrays will be untouched but their proxies
returned by .save will be consumed.
Great, thanks. I didn't even know about save... Its documentation
is hidden quite well, because I still cannot find it. Seems it is
about time I read the books.
Re: joiner: How to iterate over immutable ranges?
On Sunday, 14 February 2016 at 19:32:31 UTC, Bastiaan Veelo wrote: Thanks. I didn't know that iterating a range means mutating its contents. I still don't quite get it, and it is probably because I don't fully understand ranges. I think what confuses me the most is their analogy to containers. It's no problem to iterate over a container of immutable data, but it is for a range. Maybe this [1] will help shed some light. [1] https://www.packtpub.com/books/content/understanding-ranges
Re: joiner: How to iterate over immutable ranges?
On 02/14/2016 11:32 AM, Bastiaan Veelo wrote:
> Thanks. I didn't know that iterating a range means mutating its
> contents.
That's not the case: Just like an iterator, a range must maintain some
state to know which item is next. What needs to be mutated is that
iteration state.
> I still don't quite get it, and it is probably because I don't
> fully understand ranges. I think what confuses me the most is their
> analogy to containers.
Yes, that analogy is the wrong one (and D's slices (or dynamic arrays)
don't help with that).
> It's no problem to iterate over a container of immutable data, but
> it is for a range.
Not true. You can iterate over immutable data. In fact, a string is
nothing but a container of immutable characters yet we can iterate over it.
> I thought that joiner provided a contiguous view on distinct ranges,
> without needing to touch these. Is there another method to traverse a
> range of ranges without making copies or mutation?
Not without making copies but note that the copy that you need to make
is just the slices (i.e. views into data), which consist of just a
length and a pointer fields. If it's acceptable for you, the following
code calls .save on the elements and it works:
import std.algorithm.iteration;
import std.stdio;
import std.array;// <-- ADDED
void main()
{
immutable(string[])[] icycles;
icycles ~= ["one", "two"];
icycles ~= ["three", "four"];
foreach (number; icycles.map!(r => r.save).joiner)
writeln(number);
}
Again, .save on an array is cheap. What will happen is that the original
immutable arrays will be untouched but their proxies returned by .save
will be consumed.
Ali
Re: joiner: How to iterate over immutable ranges?
On Sunday, 14 February 2016 at 18:28:11 UTC, Jonathan M Davis wrote: An immutable range fundamentally does not work. The same goes with const. In fact, a type that's immutable is going to fail isInputRange precisely because it can't possibly function as one. While empty and front may be callable on an immutable range, depending on their exact signatures, popFront cannot be, because it has to mutate the range in order to work. Thanks. I didn't know that iterating a range means mutating its contents. I still don't quite get it, and it is probably because I don't fully understand ranges. I think what confuses me the most is their analogy to containers. It's no problem to iterate over a container of immutable data, but it is for a range. I thought that joiner provided a contiguous view on distinct ranges, without needing to touch these. Is there another method to traverse a range of ranges without making copies or mutation?
Re: joiner: How to iterate over immutable ranges?
On Sunday, February 14, 2016 15:24:39 Bastiaan Veelo via Digitalmars-d-learn
wrote:
> Hi,
>
> I am having trouble getting the iteration methods in
> std.algorithm.iteration to work on immutable data:
>
> > import std.algorithm.iteration;
> > import std.stdio;
> >
> > void main()
> > {
> > string[][] cycles;
> > cycles ~= ["one", "two"];
> > cycles ~= ["three", "four"];
> > foreach (number; cycles.joiner) // This works.
> > writeln(number);
> >
> > immutable(string[])[] icycles;
> > icycles ~= ["one", "two"];
> > icycles ~= ["three", "four"];
> > foreach (number; icycles.joiner) // Should this work?
> > writeln(number);
> > }
>
> The error message is:
>
> /d149/f840.d(15): Error: template std.algorithm.iteration.joiner
> cannot deduce function from argument types
> !()(immutable(string[])[]), candidates are:
> /opt/compilers/dmd2/include/std/algorithm/iteration.d(1911):
>std.algorithm.iteration.joiner(RoR, Separator)(RoR r, Separator
> sep) if (isInputRange!RoR && isInputRange!(ElementType!RoR) &&
> isForwardRange!Separator && is(ElementType!Separator :
> ElementType!(ElementType!RoR)))
> /opt/compilers/dmd2/include/std/algorithm/iteration.d(2194):
>std.algorithm.iteration.joiner(RoR)(RoR r) if (isInputRange!RoR
> && isInputRange!(ElementType!RoR))
>
> I had expected this to work. What did I miss?
An immutable range fundamentally does not work. The same goes with const. In
fact, a type that's immutable is going to fail isInputRange precisely
because it can't possibly function as one. While empty and front may be
callable on an immutable range, depending on their exact signatures,
popFront cannot be, because it has to mutate the range in order to work.
Arrays do typically get sliced when they're passed to functions, and array
slices are tail-const (e.g. const(int[]) is sliced as const(int)[]), so
something like
immutable string foo = "hello world";
auto result = foo.startsWith("goodbye");
will compile. But that doesn't work with ranges in general. What you're
doing is probably failing, because icycle[] is immutable(string)[], which is
immutable(char[])[], and it can't iterate over the immutable(char[]). But
regardless, if you try and use immutable with ranges, even if it works in
some cases thanks to how arrays are treated, it's just going to end up
shooting you in the foot in the end. So, I'd advise that you not bother
trying to do much with const or immutable with ranges.
- Jonathan M Davis
joiner: How to iterate over immutable ranges?
Hi,
I am having trouble getting the iteration methods in
std.algorithm.iteration to work on immutable data:
import std.algorithm.iteration;
import std.stdio;
void main()
{
string[][] cycles;
cycles ~= ["one", "two"];
cycles ~= ["three", "four"];
foreach (number; cycles.joiner) // This works.
writeln(number);
immutable(string[])[] icycles;
icycles ~= ["one", "two"];
icycles ~= ["three", "four"];
foreach (number; icycles.joiner) // Should this work?
writeln(number);
}
The error message is:
/d149/f840.d(15): Error: template std.algorithm.iteration.joiner
cannot deduce function from argument types
!()(immutable(string[])[]), candidates are:
/opt/compilers/dmd2/include/std/algorithm/iteration.d(1911):
std.algorithm.iteration.joiner(RoR, Separator)(RoR r, Separator
sep) if (isInputRange!RoR && isInputRange!(ElementType!RoR) &&
isForwardRange!Separator && is(ElementType!Separator :
ElementType!(ElementType!RoR)))
/opt/compilers/dmd2/include/std/algorithm/iteration.d(2194):
std.algorithm.iteration.joiner(RoR)(RoR r) if (isInputRange!RoR
&& isInputRange!(ElementType!RoR))
I had expected this to work. What did I miss?
Thanks,
Bastiaan.
