digitalmars.D.bugs - [Issue 7716] New: Add an indexed overload to countUntil
- d-bugmail puremagic.com (71/71) Mar 15 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7716
- d-bugmail puremagic.com (11/11) Dec 10 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7716
- d-bugmail puremagic.com (22/24) Dec 10 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7716
- d-bugmail puremagic.com (44/49) Dec 11 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7716
http://d.puremagic.com/issues/show_bug.cgi?id=7716
Summary: Add an indexed overload to countUntil
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P2
Component: Phobos
AssignedTo: nobody puremagic.com
ReportedBy: andrej.mitrovich gmail.com
--- Comment #0 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2012-03-15
09:55:27 PDT ---
Sometimes I want to find the index of a substring, but not necessarily the
index of the first occurence. E.g. in the string "foo x foo y" I want to get
the index of the second foo. Here's a simple implementation based on the
existing countUntil:
import std.algorithm : startsWith;
import std.array;
import std.traits;
sizediff_t countUntil(alias pred = "a == b", R, N)(R haystack, N needle, size_t
index)
if (is(typeof(startsWith!pred(haystack, needle))))
{
size_t count;
static if (isNarrowString!R)
{
// Narrow strings are handled a bit differently
auto length = haystack.length;
for (; !haystack.empty; haystack.popFront())
{
if (startsWith!pred(haystack, needle))
{
if (count == index)
return length - haystack.length;
else
count++;
}
}
}
else
{
typeof(return) result;
for (; !haystack.empty; ++result, haystack.popFront())
{
if (startsWith!pred(haystack, needle))
{
if (count == index)
return result;
else
count++;
}
}
}
return -1;
}
void main()
{
string s = "foo x foo y";
auto idx1 = s.countUntil("foo", 0);
auto idx2 = s.countUntil("foo", 1);
auto idx3 = s.countUntil("foo", 2);
assert(idx1 == 0);
assert(idx2 == 6);
assert(idx3 == -1);
}
Equivalent functionality could be added to std.string.indexOf to allow
case-unsensitive searches.
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Andrej Mitrovic <andrej.mitrovich gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |WONTFIX
--- Comment #1 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2012-12-10
14:51:28 PST ---
This niche feature belongs in user-space libraries, not Phobos.
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bearophile_hugs eml.cc changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bearophile_hugs eml.cc
--- Comment #2 from bearophile_hugs eml.cc 2012-12-10 15:28:19 PST ---
This belongs in Phobos. See Python string functions, that have optional
start-end:
help(str.find)
Help on method_descriptor:
find(...)
S.find(sub [,start [,end]]) -> int
Return the lowest index in S where substring sub is found,
such that sub is contained within s[start:end]. Optional
arguments start and end are interpreted as in slice notation.
Return -1 on failure.
help(str.index)
Help on method_descriptor:
index(...)
S.index(sub [,start [,end]]) -> int
Like S.find() but raise ValueError when the substring is not found.
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monarchdodra gmail.com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |monarchdodra gmail.com
--- Comment #3 from monarchdodra gmail.com 2012-12-11 05:30:54 PST ---
(In reply to comment #0)
Sometimes I want to find the index of a substring, but not necessarily the
index of the first occurence. E.g. in the string "foo x foo y" I want to get
the index of the second foo.
This would conflict with this other request:
http://d.puremagic.com/issues/show_bug.cgi?id=5507
which would allow counting until multiple needles, eg:
//----
string s = "foo x bar y";
size_t index = s.countUntil("bar", 'x');
assert(index == 4);
//----
So what you are asking for may have to be implemented as "countUntilN" or
something:
//-----
string s = "foo x bar y";
size_t index = s.countUntilN(1, "bar", 'x');
assert(index == 6); //First found 'x', then found "bar".
//-----
Here's a simple implementation based on the
existing countUntil:
Just want to point out that that implementation is based on an old and buggy
implementation of countUntil. 2 problems:
1. No support for reference type ranges.
2. Incorrect support of unicode.
The issue 1 is not that big of an issue, but is unacceptable of a standard
library.
Issue 2 depends on what you want. Do you want the *index* in the string, or the
logical *range_position*:
"日本語".countUntil(本); //1 popFront once
"日本語".countUntil(本); //3 slice index: "日本語"[3 .. $]
If you plan on using countUntil(N), then I'd recommend basing your
implementation on https://github.com/D-Programming-Language/phobos/pull/951
Finally, keep in mind that the standard function "count" skips over overlaps:
"ababab".count("abab"); //produces 1. Only 1 match.
However, your countUntil implementation would find that second match:
"ababab".countUntilN(1, "abab"); //Produces 2
This would be kind of weird:
"Given a range which holds 1 instance of a needle, countUntilN is capable of
finding the second occurrence of said needle :/"
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