Re: writeln wipes contents of variables ?
On Friday, 22 January 2016 at 01:49:58 UTC, anonymous wrote: On 22.01.2016 01:49, W.J. wrote: How can I identify those ranges, or, how can I tell if any particular range has value semantics ? I didn't read any of this in the manual - not that I could remember anyways. Generally you shouldn't. If you care about it either way, use .save or std.range.refRange. If you don't want some range r to be consumed by some operation, pass r.save instead of plain r. If you want r to be consumed, pass refRange(&r). Only if you don't care if r is consumed or not, should you pass simply r. If you know for a fact that copying r is the same as r.save, then you can just pass (and copy) r, of course. We know it's that way with dynamic arrays, because of their nature as pointer+length structures. But there's nothing wrong with calling .save on an array anyway. Also, when a function takes a range via a ref parameter, then you don't need refRange, of course. The ref parameter ensures that no copy is made and that the original range is affected by the function. This is even better than trying to figure out whether value semantics are supported or not. So, .safe returns a copy of the range - I suppose a copy of the current state - and refRange always consumes the values in the range. Thanks a lot for your reply! Very much appreciated.
Re: writeln wipes contents of variables ?
On Friday, 22 January 2016 at 01:47:19 UTC, Rikki Cattermole wrote: Contrary to what it is called in the links, this is a NewsGroup/Mailing list and not a forum. So no editing ability :) I'll keep that in mind. Thanks :)
Re: writeln wipes contents of variables ?
On 22.01.2016 01:49, W.J. wrote: How can I identify those ranges, or, how can I tell if any particular range has value semantics ? I didn't read any of this in the manual - not that I could remember anyways. Generally you shouldn't. If you care about it either way, use .save or std.range.refRange. If you don't want some range r to be consumed by some operation, pass r.save instead of plain r. If you want r to be consumed, pass refRange(&r). Only if you don't care if r is consumed or not, should you pass simply r. If you know for a fact that copying r is the same as r.save, then you can just pass (and copy) r, of course. We know it's that way with dynamic arrays, because of their nature as pointer+length structures. But there's nothing wrong with calling .save on an array anyway. Also, when a function takes a range via a ref parameter, then you don't need refRange, of course. The ref parameter ensures that no copy is made and that the original range is affected by the function.
Re: writeln wipes contents of variables ?
On 22/01/16 5:45 AM, W.J. wrote: On Thursday, 21 January 2016 at 14:36:36 UTC, Rikki Cattermole wrote: On 22/01/16 3:07 AM, W.J. wrote: On Thursday, 21 January 2016 at 13:15:46 UTC, Rikki Cattermole wrote: [...] Thanks for your reply. So writeln consumes the values in an InputRange. That leads me to believe that if I feed an InputRange to foreach, it will consume the values, too. Did I get that right ? Correct. If that's the case, why I can iterate and write the values just fine using nested foreach loops *and* writeln them afterwards ? I would expect the foreach loops leaves "step3" in the same state as writeln does. So I'm still a little confused as to how foreach goes about it. I thought foreach would be iterating an InputRange the same way writeln does. By attaching ".array" to the result of I was under the impression the result was actually converted to an array. That seems not to be the case. What I probably got was something like an array of arrays of groups - which are apparently InputRanges ? So, yes, writeln... InputRange... makes perfect sense except for the foreach case. Thanks again for the help :) After playing around some more and apart from requiring much more practice I think this topic can be marked as 'solved'. However, I can't seem to find the edit button for my initial post. Anyways, thanks for your contributions :) Very much appreciated! Contrary to what it is called in the links, this is a NewsGroup/Mailing list and not a forum. So no editing ability :)
Re: writeln wipes contents of variables ?
On Thursday, 21 January 2016 at 21:59:10 UTC, Chris Wright wrote: On Thu, 21 Jan 2016 14:07:16 +, W.J. wrote: So writeln consumes the values in an InputRange. That leads me to believe that if I feed an InputRange to foreach, it will consume the values, too. Did I get that right ? In general, yes. Thanks for your reply. Some ranges have value semantics and can be saved simply by assigning them to a new variable, or passing them to a function. How can I identify those ranges, or, how can I tell if any particular range has value semantics ? I didn't read any of this in the manual - not that I could remember anyways. Thanks for your help!
Re: writeln wipes contents of variables ?
On Thu, 21 Jan 2016 14:07:16 +, W.J. wrote: > So writeln consumes the values in an InputRange. That leads me to > believe that if I feed an InputRange to foreach, it will consume the > values, too. > Did I get that right ? In general, yes. Some ranges have value semantics and can be saved simply by assigning them to a new variable, or passing them to a function.
Re: writeln wipes contents of variables ?
On Thursday, 21 January 2016 at 14:36:36 UTC, Rikki Cattermole wrote: On 22/01/16 3:07 AM, W.J. wrote: On Thursday, 21 January 2016 at 13:15:46 UTC, Rikki Cattermole wrote: [...] Thanks for your reply. So writeln consumes the values in an InputRange. That leads me to believe that if I feed an InputRange to foreach, it will consume the values, too. Did I get that right ? Correct. If that's the case, why I can iterate and write the values just fine using nested foreach loops *and* writeln them afterwards ? I would expect the foreach loops leaves "step3" in the same state as writeln does. So I'm still a little confused as to how foreach goes about it. I thought foreach would be iterating an InputRange the same way writeln does. By attaching ".array" to the result of I was under the impression the result was actually converted to an array. That seems not to be the case. What I probably got was something like an array of arrays of groups - which are apparently InputRanges ? So, yes, writeln... InputRange... makes perfect sense except for the foreach case. Thanks again for the help :) After playing around some more and apart from requiring much more practice I think this topic can be marked as 'solved'. However, I can't seem to find the edit button for my initial post. Anyways, thanks for your contributions :) Very much appreciated!
Re: writeln wipes contents of variables ?
On 22/01/16 3:07 AM, W.J. wrote: On Thursday, 21 January 2016 at 13:15:46 UTC, Rikki Cattermole wrote: Ok so input ranges. An input range is a little bit like an iterator (if you know what that is). When an input range has been read fully, it is empty aka no longer has any values associated with it. writeln, reads an input range fully (since you can't ask for what is next without removing the current item) and outputs each entry. So yes, writeln will remove all entries from an input range. Note however it will not do this for arrays since you can read anywhere within them. Thanks for your reply. So writeln consumes the values in an InputRange. That leads me to believe that if I feed an InputRange to foreach, it will consume the values, too. Did I get that right ? Correct. If that's the case, why I can iterate and write the values just fine using nested foreach loops *and* writeln them afterwards ? I would expect the foreach loops leaves "step3" in the same state as writeln does. So I'm still a little confused as to how foreach goes about it. I thought foreach would be iterating an InputRange the same way writeln does. By attaching ".array" to the result of I was under the impression the result was actually converted to an array. That seems not to be the case. What I probably got was something like an array of arrays of groups - which are apparently InputRanges ? So, yes, writeln... InputRange... makes perfect sense except for the foreach case. Thanks again for the help :)
Re: writeln wipes contents of variables ?
On Thursday, 21 January 2016 at 13:15:46 UTC, Rikki Cattermole wrote: Ok so input ranges. An input range is a little bit like an iterator (if you know what that is). When an input range has been read fully, it is empty aka no longer has any values associated with it. writeln, reads an input range fully (since you can't ask for what is next without removing the current item) and outputs each entry. So yes, writeln will remove all entries from an input range. Note however it will not do this for arrays since you can read anywhere within them. Thanks for your reply. So writeln consumes the values in an InputRange. That leads me to believe that if I feed an InputRange to foreach, it will consume the values, too. Did I get that right ? If that's the case, why I can iterate and write the values just fine using nested foreach loops *and* writeln them afterwards ? I would expect the foreach loops leaves "step3" in the same state as writeln does. So I'm still a little confused as to how foreach goes about it. I thought foreach would be iterating an InputRange the same way writeln does. By attaching ".array" to the result of I was under the impression the result was actually converted to an array. That seems not to be the case. What I probably got was something like an array of arrays of groups - which are apparently InputRanges ? So, yes, writeln... InputRange... makes perfect sense except for the foreach case. Thanks again for the help :)
Re: writeln wipes contents of variables ?
On 22/01/16 2:11 AM, W.J. wrote:
Hi everybody!
I'm new to D and trying to wrap my head around ranges.
For a start I'm trying to take a input string and transform it, group
it, etc.
After each step I inspect the result.
It works fine until step 3 where all of a sudden, after write(ln)ing the
result, "step3" holds an array of empty arrays.
What gives? Program and output are attached below.
My question is why are "step3"'s contents before and after the writeln
(1) different?
If I remove this line at (1) the foreach loops print the contents as I'd
expect and the following writeln (2) prints the contents as expected, too.
However the writeln (3) prints empty arrays again.
I don't understand this behavior and I'd really like to know what's
going on.
Your help and time is much appreciated!
I'm using an unmodified local build of dmd, druntime, and phobos from
github updated and recompiled today.
[code]
import std.range;
import std.stdio;
import std.algorithm;
void main() {
string test = "@\r node1\nnodea\r\nkey:val\n\n node2\n
nodea\n";
writeln(test);
writeln("---");
auto step1 = test.replace("\r\n", "\n")
.replace(" ", "\t")
.splitter!"a == 10 || a == 13"()
;
writeln("Step 1:", step1);
writeln("---");
writeln(" type: ", typeid(step1));
writeln("---");
import std.typecons: Tuple;
string[][] step2;
foreach(a; step1) {
auto e = findSplitAfter(a, "\t").array;
step2 ~= e;
}
writeln("Step 2:", step2);
writeln("---");
writeln(" type: ", typeid(step2));
writeln("---");
auto step3 = step2.chunkBy!((a,b) => a[0]==b[0]).array;
writeln("Step 3:", step3); // (1)
writeln("---");
writeln(" type: ", typeid(step3));
writeln("-+-");
foreach(x; step3) {
writeln("x:",typeid(x),x);
foreach(y; x)
writeln(" y:",typeid(y),y);
}
writeln("--",step3); // (2)
writeln("--",step3); // (3)
writeln("the end");
}
[/code]
Output:
[code]
node1
nodea
key:val
node2
nodea
---
Step 1:["@", "\tnode1", "\t\tnodea", "\t\tkey:val", "", "\tnode2",
"\t\tnodea", ""]
---
type: std.algorithm.iteration.SplitterResult!(unaryFun,
string).SplitterResult
---
Step 2:[["", "@"], ["\t", "node1"], ["\t", "\tnodea"], ["\t",
"\tkey:val"], ["", ""], ["\t", "node2"], ["\t", "\tnodea"], ["", ""]]
---
type: immutable(char)[][][]
---
Step 3:[[["", "@"]], [["\t", "node1"], ["\t", "\tnodea"], ["\t",
"\tkey:val"]], [["", ""]], [["\t", "node2"], ["\t", "\tnodea"]], [["",
""]]]
---
type: app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
-+-
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
--[[], [], [], [], []]
the end
[/code]
Ok so input ranges.
An input range is a little bit like an iterator (if you know what that is).
When an input range has been read fully, it is empty aka no longer has
any values associated with it.
writeln, reads an input range fully (since you can't ask for what is
next without removing the current item) and outputs each entry.
So yes, writeln will remove all entries from an input range.
Note however it will not do this for arrays since you can read anywhere
within them.
