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std.algorithm: Document sort's predicate expectations

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Vladimir Panteleev 2013-11-13 20:54:04 +00:00
parent 33114ec2ea
commit 2399976e1b
1 changed files with 11 additions and 0 deletions
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std/algorithm.d
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@ -8791,6 +8791,17 @@ wrapper around the original range, so both it and the original range are sorted,
but other functions won't know that the original range has been sorted, whereas
they $(I can) know that $(XREF range, SortedRange) has been sorted.
The predicate is expected to satisfy certain rules in order for $(D sort) to
behave as expected - otherwise, the program may fail on certain inputs (but not
others) when not compiled in release mode, due to the cursory $(D assumeSorted)
check. Specifically, $(D sort) expects $(D less(a,b) && less(b,c)) to imply
$(D less(a,c)) (transitivity), and, conversely, $(D !less(a,b) && !less(b,c)) to
imply $(D !less(a,c)). Note that the default predicate ($(D "a < b")) does not
always satisfy these conditions for floating point types, because the expression
will always be $(D false) when either $(D a) or $(D b) is NaN.
See_Also:
$(XREF range, assumeSorted)$(BR)
STL's $(WEB sgi.com/tech/stl/_sort.html, _sort)$(BR)