On Saturday, 6 August 2016 at 23:00:42 UTC, Alex wrote:
Hi all... a technical question from my side...
why the last line of the following gives the error?
import std.stdio;
import std.range;
import std.algorithm;
void main()
{
size_t[][] darr;
darr.length = 2;
darr[0] = [0, 1, 2, 3];
darr[1] = [4, 5, 6];
auto fT = frontTransversal(darr);
assert(equal(fT, [ 0, 4 ][]));
auto heads = assumeSorted!"a <= b"(fT);
writeln(heads.lowerBound(3)); //!(SearchPolicy.gallop)
}
The error is:
Error: template
std.range.SortedRange!(FrontTransversal!(ulong[][],
cast(TransverseOptions)0), "a <= b").SortedRange.lowerBound
cannot deduce function from argument types !()(int), candidates
are:
package.d(7807,10):
std.range.SortedRange!(FrontTransversal!(ulong[][],
cast(TransverseOptions)0), "a <=
b").SortedRange.lowerBound(SearchPolicy sp =
SearchPolicy.binarySearch, V)(V value) if
(isTwoWayCompatible!(predFun, ElementType!Range, V) &&
hasSlicing!Range)
I tried also with "assumeNotJagged" for the FrontTransversal,
it didn't worked either, beyond the fact, that assumeNotJagged
is not of interest for me...
Unfortunately, frontTraversal is not giving you a random access
range, only a bidirectional range, which means it does not
support indexing or slicing. It appears that the TraversalOptions
doesn't cover the case where each range is "long enough" to be
indexed but not equal length.
static assert(isBidirectionalRange!(typeof(fT))); // succeeds
static assert(isRandomAccessRange!(typeof(fT))); // fails
static assert(__traits(compiles, fT[0])); // fails
static assert(__traits(compiles, fT[0 .. 2]));// fails
In the mean time, you can use this simple alternative:
auto fT = darr.map!front; // for arrays
auto fT = darr.map!"a.front"; // for any range
