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digitalmars.D.bugs - [Issue 7839] New: std.range.count() too

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7839

           Summary: std.range.count() too
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc



I'd like a count() in std.range. It's similar to the generator with the same
name in the Python itertools module:
http://docs.python.org/library/itertools.html#itertools.count

a count() is also useful with bigints, where you can't replace it with
iota(BigInt.max).


A bare-bones implementation that shows it basic semantics (but it's useful to
add few more methods):


struct Count(T) {
    T n;
    this(T n_) { this.n = n_; }
    const bool empty = false;
     property T front() { return n; }
    void popFront() { /* n++; */ n += 1; }
}

// Two helper functions
Count!T count(T)(T start) { return Count!T(start); }
Count!T count(T)() { return Count!T(cast(T)0); }

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Apr 05 2012
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7839




And answer to a question by jerro in D.learn:

http://forum.dlang.org/thread/4F949E90.9060700 webdrake.net#post-evdrwckxsqieyrweuxzp:40forum.dlang.org


 Couldn't it just be iota with no parameters?


The Count range has a helper count() function similar to this, that's meant to
have an argument that defaults to zero:

Count!T count(T)(T start=0) if (isIntegral!T) { return Count!T(start); }

The argument allows it to start from another starting point, and it allows you
to specify the type of the numbers it yields, while in iota() without arguments
it's less easy to specify the type of the numbers it yields.

Count(5) is easy to replace with iota(5, int.max), but count(BigInt(0)) is less
easy to replace with iota, because it doesn't give you a way to denote a
right-open BigInt interval. And using iota(BigInt(0), BigInt(ulong.max)) is not
that good. Currently using BigInt in iota seems to not even being supported.

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Apr 23 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7839




std.algorithm has a function named count(), so this range will need a different
name. Maybe countFrom()?

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Apr 24 2012
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7839


bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|std.range.count() too       |std.range.countFrom() too



Changed the name of this issue from "std.range.count() too" to
"std.range.countFrom() too".

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