digitalmars.D.bugs - [Issue 4535] New: std.range could have a takeWhile!pred(range) function
- d-bugmail puremagic.com (68/68) Jul 30 2010 http://d.puremagic.com/issues/show_bug.cgi?id=4535
- d-bugmail puremagic.com (10/10) Aug 14 2010 http://d.puremagic.com/issues/show_bug.cgi?id=4535
- d-bugmail puremagic.com (18/18) Aug 14 2010 http://d.puremagic.com/issues/show_bug.cgi?id=4535
- d-bugmail puremagic.com (21/22) Aug 19 2010 http://d.puremagic.com/issues/show_bug.cgi?id=4535
- d-bugmail puremagic.com (10/10) Jan 09 2011 http://d.puremagic.com/issues/show_bug.cgi?id=4535
- d-bugmail puremagic.com (10/10) Jun 04 2011 http://d.puremagic.com/issues/show_bug.cgi?id=4535
http://d.puremagic.com/issues/show_bug.cgi?id=4535 Summary: std.range could have a takeWhile!pred(range) function Product: D Version: D2 Platform: All OS/Version: All Status: NEW Severity: enhancement Priority: P2 Component: Phobos AssignedTo: nobody puremagic.com ReportedBy: philippe.sigaud gmail.com 11:49:25 CEST --- takeWhile!predicate(range) is a very useful function, that lazily produces elements of a range, as long as a predicate holds for the produced elements. Usage example: ---- auto small = takeWhile!"a<5"([0,1,2,3,4,5,6,7,6,5,4,3,2,1,0]); assert(equal(small, [0,1,2,3,4,5]); ---- That's different from filter!predicate(range) that would return _all_ elements in the range that satisfy the predicate. Possible code for this follow: import std.functional: unaryFun; import std.range; struct TakeWhile(alias pred, R) if (isInputRange!R && is(typeof(!unaryFun!pred(ElementType!R.init)) == bool)) { R _range; bool empty() property { return _range.empty || !(unaryFun!pred(_range.front)); } ElementType!R front() property { return _range.front; } TakeWhile save() property { return this; } void popFront() { _range.popFront; } } TakeWhile!(pred, R) takeWhile(alias pred, R)(R range) if (isInputRange!R) { return TakeWhile!(pred,R)(range); } unittest { auto arr = [0,1,2,3,4,3,2,1,0]; // With 'string functions' assert(equal( takeWhile!"a<3"(arr), [0,1,2])); // standard case assert(equal( takeWhile!"a<10"(arr), arr)); // predicate true for all elements assert(takeWhile!"a<0"(arr).empty); // predicate false from the beginning assert(takeWhile!"a!=0"(arr).empty); // predicate false for the first element // With a standard function bool foo(int i) { return i != 4;} assert(equal( takeWhile!foo(arr), [0,1,2,3])); } -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 30 2010
http://d.puremagic.com/issues/show_bug.cgi?id=4535 David Simcha <dsimcha yahoo.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |dsimcha yahoo.com Doesn't std.algorithm.until pretty much do what you want? -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Aug 14 2010
http://d.puremagic.com/issues/show_bug.cgi?id=4535 Jonathan M Davis <jmdavisProg gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |jmdavisProg gmail.com 18:45:43 PDT --- I'd say that it mostly does, but it's not generic enough. until() has the concept of a sentinel, while takeWhile() is based entirely on a predicate. I'm not quite sure how their implementations would be different, but I'd expect takeWhile() to be at least slightly more efficient (though perhaps negligably so) than until(). I think that it would be beneficial to have the more generic takeWhile(); if nothing else, the intent is clearer. Of course, truth be told, I'm not a huge fan of until() anyway. I really think that it should be more like find() except return what's before what you're looking for rather than starting with it like find() does. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Aug 14 2010
http://d.puremagic.com/issues/show_bug.cgi?id=4535 00:46:32 CEST ---Doesn't std.algorithm.until pretty much do what you want?Hmm. I see until() is templated on the predicate. I guess most of the time, I can rewrite my predicates to use until. auto t = takeWhile!"a*a>10"(someValues); auto u = until!"a*a>b"(10, someValues); // hey, b is 10, a will be elements from someValues. Is that clear? I personally find takeWhile to be more readable. Maybe I'm biased due to my using it in other languages? Also, it's cumbersome for no-arg functions: // takes lines as long as they are not empty auto t = takeWhile!"!a.empty"(file.byLine); auto u = until!"!a.empty"(dummy, file.byLine); auto t = takeWile!externalUnaryPredicate(someValues); auto u = until!externalUnaryPredicate(??, someValues); // How do I do that? Philippe -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Aug 19 2010
http://d.puremagic.com/issues/show_bug.cgi?id=4535 Andrei Alexandrescu <andrei metalanguage.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |ASSIGNED CC| |andrei metalanguage.com AssignedTo|nobody puremagic.com |andrei metalanguage.com -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jan 09 2011
http://d.puremagic.com/issues/show_bug.cgi?id=4535 timon.gehr gmx.ch changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |timon.gehr gmx.ch *** Issue 6104 has been marked as a duplicate of this issue. *** -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jun 04 2011