V Tue, 29 Dec 2015 17:42:26 +0000
Alex Parrill via Digitalmars-d-learn
<digitalmars-d-learn@puremagic.com> napsáno:
> On Tuesday, 29 December 2015 at 09:26:31 UTC, Alex wrote:
> > The problem is, that the last line with the reduce does not
> > compile. Why?
>
> If you get an error, it is imperative that you tell us what it is.
>
> For the record, this code:
>
> import std.bitmanip;
> import std.stdio;
> import std.algorithm;
>
> void main() {
>
> BitArray[] arr7 = [BitArray([0, 1, 0, 1, 0, 1]),
> BitArray([0, 1, 0, 0, 0, 0]), BitArray([0, 1, 0, 1, 0, 0]),
> BitArray([0, 1, 0, 1, 0, 0])];
>
> BitArray common = BitArray([1,1,1,1,1,1]);
> foreach(BitArray ba; arr7)
> {
> common &= ba;
> }
> writeln("common2: ", common);
>
> writeln("common1: ", reduce!((a,b) => a & b)(arr7));
> }
>
> Gives me the error:
>
> /opt/compilers/dmd2/include/std/algorithm/iteration.d(2570):
> Error: variable f868.main.F!(__lambda1).e cannot be declared to
> be a function
> /opt/compilers/dmd2/include/std/meta.d(546): Error: template
> instance f868.main.F!(__lambda1) error instantiating
> /opt/compilers/dmd2/include/std/algorithm/iteration.d(2477):
> instantiated from here: staticMap!(ReduceSeedType, __lambda1)
> /d486/f868.d(16): instantiated from here:
> reduce!(BitArray[])
> /d486/f868.d(16): Error: template std.algorithm.iteration.reduce
> cannot deduce function from argument types !((a, b) => a &
> b)(BitArray[]), candidates are:
> /opt/compilers/dmd2/include/std/algorithm/iteration.d(2451):
> std.algorithm.iteration.reduce(fun...) if (fun.length >= 1)
>
> On 2.069.1 (dpaste: http://dpaste.dzfl.pl/8d7652e7ebeb). I don't
> have time ATM to diagnose it further. It definitely shouldn't be
> that cryptic of an error message.
It is cause by this
https://dlang.org/phobos/std_bitmanip.html#.BitArray.init
So until it will be removed it will does not compile.
Problem is in
https://dlang.org/phobos/std_range_primitives.html#.ElementType
which is implementet as
template ElementType(R)
{
static if (is(typeof(R.init.front.init) T))
alias ElementType = T;
else
alias ElementType = void;
}
maybe rewriting this like:
template ElementType(R)
{
static if (is(typeof(R.init.front) T))
alias ElementType = T;
else
alias ElementType = void;
}
could help too
