Fix lexicographical ordering of sequences #8400
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added 7 commits
August 8, 2013 22:07
Use Eq + Ord for lexicographical ordering of sequences.
For each of <, <=, >= or > as R, use::
[x, ..xs] R [y, ..ys] = if x != y { x R y } else { xs R ys }
Previous code using `a < b` and then `!(b < a)` for short-circuiting
fails on cases such as [1.0, 2.0] < [0.0/0.0, 3.0], where the first
element was effectively considered equal.
(A,) did not have the trait implementations of 2- to 12- tuples.
Use the definition, where R is <, <=, >=, or >
[x, ..xs] R [y, ..ys] = if x != y { x R y } else { xs R ys }
Previously, tuples would only implement < and derive the other
comparisons from it; this is incorrect. Included are several testcases
involving NaN comparisons that are now correct.
Previously, tuples would consider an element equal if both a < b and
b < a were false, this was also incorrect.
added 2 commits
August 8, 2013 23:07
Just like the Ord methods, Eq::ne needs to be implemented in terms of the same operation on the elements.
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This looks good to me, and it seems well-tested. |
bors
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Aug 12, 2013
Use Eq + Ord for lexicographical ordering of sequences.
For each of <, <=, >= or > as R, use::
[x, ..xs] R [y, ..ys] = if x != y { x R y } else { xs R ys }
Previous code using `a < b` and then `!(b < a)` for short-circuiting
fails on cases such as [1.0, 2.0] < [0.0/0.0, 3.0], where the first
element was effectively considered equal.
Containers like &[T] did also implement only one comparison operator `<`,
and derived the comparison results from this. This isn't correct either for
Ord.
Implement functions in `std::iterator::order::{lt,le,gt,ge,equal,cmp}` that all
iterable containers can use for lexical order.
We also visit tuple ordering, having the same problem and same solution
(but differing implementation).
flip1995
pushed a commit
to flip1995/rust
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Feb 10, 2022
Split matches Part of rust-lang#6680 changelog: None
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Use Eq + Ord for lexicographical ordering of sequences.
For each of <, <=, >= or > as R, use::
Previous code using
a < band then!(b < a)for short-circuitingfails on cases such as [1.0, 2.0] < [0.0/0.0, 3.0], where the first
element was effectively considered equal.
Containers like &[T] did also implement only one comparison operator
<,and derived the comparison results from this. This isn't correct either for
Ord.
Implement functions in
std::iterator::order::{lt,le,gt,ge,equal,cmp}that alliterable containers can use for lexical order.
We also visit tuple ordering, having the same problem and same solution
(but differing implementation).