digitalmars.D.bugs - [Issue 6383] New: Unpacking from dynamic array, lazy ranges
- d-bugmail puremagic.com (102/112) Jul 26 2011 http://d.puremagic.com/issues/show_bug.cgi?id=6383
- d-bugmail puremagic.com (8/8) Jul 26 2011 http://d.puremagic.com/issues/show_bug.cgi?id=6383
- d-bugmail puremagic.com (15/19) Jul 30 2011 http://d.puremagic.com/issues/show_bug.cgi?id=6383
- d-bugmail puremagic.com (8/19) Jul 30 2011 http://d.puremagic.com/issues/show_bug.cgi?id=6383
- d-bugmail puremagic.com (7/22) Jul 30 2011 http://d.puremagic.com/issues/show_bug.cgi?id=6383
- d-bugmail puremagic.com (13/24) Dec 21 2011 http://d.puremagic.com/issues/show_bug.cgi?id=6383
http://d.puremagic.com/issues/show_bug.cgi?id=6383
Summary: Unpacking from dynamic array, lazy ranges
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: DMD
AssignedTo: nobody puremagic.com
ReportedBy: bearophile_hugs eml.cc
--- Comment #0 from bearophile_hugs eml.cc 2011-07-26 06:52:19 PDT ---
This is a spinoff of Issue 6365 (AutoTupleDeclaration).
Issue 6365 is about syntax sugar to unpack tuples, but unpacking dynamic arrays
or lazy ranges too is handy and commonly useful, because in D most arrays are
not fixed-sized, and many functions return a lazy range, like lazy splitting,
regular expression matches, etc.
The 'lengths don't match' exception is already present in D and I think it's
acceptable (when the lengths are statically known there is no need to test
lengths at run time, so this exception throwing is not present, so it's nothrow
code):
int[] array = [1, 2, 3];
int[2] a2 = array[];
-------------------
Some usage examples, assign from a dynamic array, in D2:
import std.string;
void main() {
auto s = " foo bar ";
auto ss = s.split();
auto sa = ss[0];
auto sb = ss[1];
}
In Python2.6:
sa, sb = " foo bar ".split()
sa
'foo'
sb
'bar'
Proposed:
import std.string;
void main() {
auto s = " foo bar ";
auto (sa, sb) = s.split();
}
-------------------
From lazy range, D2:
import std.algorithm, std.conv, std.string;
void main() {
string s = " 15 27";
// splitter doesn't work yet for this
// (here it doesn't strip the leading space)
//auto xy = map!(to!int)(splitter(s));
auto xy = map!(to!int)(split(s));
int x = xy[0];
int y = xy[1];
}
In Python:
x, y = map(int, " 15 27".split())
x
15
y
27
from itertools import imap
x, y = imap(int, " 15 27".split())
x
15
y
27
Proposed:
import std.algorithm, std.conv, std.string;
void main() {
string s = " 15 27";
(int x, int y) = map!(to!int)(splitter(s));
}
-------------------
From a lazy range, another example. See:
http://rosettacode.org/wiki/Range_expansion#D
D2 code:
import std.stdio, std.regex, std.string, std.conv, std.range;
int[] rangeExpand(string txt) {
int[] result;
foreach (r; std.string.split(txt, ",")) {
auto m = array(match(r, r"^(-?\d+)(-?(-?\d+))?$").captures);
if (m[2].empty)
result ~= to!int(m[1]);
else
result ~= array(iota(to!int(m[1]), to!int(m[3])+1));
}
return result;
}
Python:
import re
def rangeexpand(txt):
lst = []
for rng in txt.split(','):
start,end = re.match('^(-?\d+)(?:-(-?\d+))?$', rng).groups()
if end:
lst.extend(xrange(int(start),int(end)+1))
else:
lst.append(int(start))
return lst
print(rangeexpand('-6,-3--1,3-5,7-11,14,15,17-20'))
Proposed (just the important line), from dynamic array:
auto (start,end) = array(match(r, r"^(-?\d+)(-?(-?\d+))?$").captures);
Or better, from the range of regex captures:
auto (start,end) = match(r, r"^(-?\d+)(-?(-?\d+))?$").captures;
Similar unpacking from Python list (that is a dynamic array) or from lazy
iterable is quite common in scripting-style Python code.
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Jul 26 2011
d-bugmail puremagic.com http://d.puremagic.com/issues/show_bug.cgi?id=6383 --- Comment #1 from bearophile_hugs eml.cc 2011-07-26 06:57:08 PDT --- Sorry, this is not correct: auto (start,end) = array(match(r, r"^(-?\d+)(-?(-?\d+))?$").captures); auto (start,end) = match(r, r"^(-?\d+)(-?(-?\d+))?$").captures; -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 26 2011
http://d.puremagic.com/issues/show_bug.cgi?id=6383
Dmitry Olshansky <dmitry.olsh gmail.com> changed:
What |Removed |Added
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CC| |dmitry.olsh gmail.com
--- Comment #2 from Dmitry Olshansky <dmitry.olsh gmail.com> 2011-07-30
08:36:58 PDT ---
(In reply to comment #1)
Sorry, this is not correct:
auto (start,end) = array(match(r, r"^(-?\d+)(-?(-?\d+))?$").captures);
auto (start,end) = match(r, r"^(-?\d+)(-?(-?\d+))?$").captures;
I'm puzzled, in this case captures contain way more then 2 strings:
0 - whole match
1 - (-?\d+)
2 - (-?(-?\d+))?
3 - (-?\d+)
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Jul 30 2011
http://d.puremagic.com/issues/show_bug.cgi?id=6383 --- Comment #3 from bearophile_hugs eml.cc 2011-07-30 08:42:48 PDT --- (In reply to comment #2)(In reply to comment #1)What are you puzzled about? I have already said that code I have written is not correct. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------Sorry, this is not correct: auto (start,end) = array(match(r, r"^(-?\d+)(-?(-?\d+))?$").captures); auto (start,end) = match(r, r"^(-?\d+)(-?(-?\d+))?$").captures;I'm puzzled, in this case captures contain way more then 2 strings: 0 - whole match 1 - (-?\d+) 2 - (-?(-?\d+))? 3 - (-?\d+)
Jul 30 2011
http://d.puremagic.com/issues/show_bug.cgi?id=6383 --- Comment #4 from Dmitry Olshansky <dmitry.olsh gmail.com> 2011-07-30 08:43:44 PDT --- (In reply to comment #3)(In reply to comment #2)Ah, don't worry, I supposed you pasted a correction, sily me. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------(In reply to comment #1)What are you puzzled about? I have already said that code I have written is not correct.Sorry, this is not correct: auto (start,end) = array(match(r, r"^(-?\d+)(-?(-?\d+))?$").captures); auto (start,end) = match(r, r"^(-?\d+)(-?(-?\d+))?$").captures;I'm puzzled, in this case captures contain way more then 2 strings: 0 - whole match 1 - (-?\d+) 2 - (-?(-?\d+))? 3 - (-?\d+)
Jul 30 2011
http://d.puremagic.com/issues/show_bug.cgi?id=6383
pompei2 gmail.com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |pompei2 gmail.com
--- Comment #5 from pompei2 gmail.com 2011-12-21 00:38:37 PST ---
I think this would be very useful.(In reply to comment #2)
(In reply to comment #1)
Sorry, this is not correct:
auto (start,end) = array(match(r, r"^(-?\d+)(-?(-?\d+))?$").captures);
auto (start,end) = match(r, r"^(-?\d+)(-?(-?\d+))?$").captures;
I'm puzzled, in this case captures contain way more then 2 strings:
0 - whole match
1 - (-?\d+)
2 - (-?(-?\d+))?
3 - (-?\d+)
So why couldn't "start" and "end" unpack the whole match and (-?\d+) and ignore
the last two?
I totally want to see unpacking in D2.
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Dec 21 2011