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digitalmars.D.learn - SortedRange.lowerBound from FrontTransversal

reply Alex <sascha.orlov gmail.com> writes:
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...
Aug 06 2016
parent reply Michael Coulombe <kirsybuu gmail.com> writes:
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
Aug 07 2016
parent reply Michael Coulombe <kirsybuu gmail.com> writes:
On Monday, 8 August 2016 at 00:57:41 UTC, Michael Coulombe wrote:

 ...


And looking at the source, the reason it fails when using 
TransverseOptions.assumeNotJagged is that it does not implement 
length or $.

I made this into an enhancement request: 
https://issues.dlang.org/show_bug.cgi?id=16363
Aug 07 2016
parent Alex <sascha.orlov gmail.com> writes:
On Monday, 8 August 2016 at 01:36:43 UTC, Michael Coulombe wrote:

 On Monday, 8 August 2016 at 00:57:41 UTC, Michael Coulombe 
 wrote:

 ...


 And looking at the source, the reason it fails when using 
 TransverseOptions.assumeNotJagged is that it does not implement 
 length or $.

 I made this into an enhancement request: 
 https://issues.dlang.org/show_bug.cgi?id=16363


Ah... ok...
Thanks!
Aug 08 2016