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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
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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 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. 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: See_Also:
$(XREF range, assumeSorted)$(BR) $(XREF range, assumeSorted)$(BR)
STL's $(WEB sgi.com/tech/stl/_sort.html, _sort)$(BR) STL's $(WEB sgi.com/tech/stl/_sort.html, _sort)$(BR)