60 lines
1.5 KiB
Plaintext
60 lines
1.5 KiB
Plaintext
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== Why is this an issue?
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Manually implementing `PartialOrd` for a type that derives `Ord` can lead to inconsistencies, as the implementations of these traits must agree for sorting and other comparisons. According to the trait contract, the following must hold for any type implementing `Ord`:
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[source,rust]
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----
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k1.cmp(&k2) == k1.partial_cmp(&k2).unwrap()
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----
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Using a default-generated `Ord` implementation with an explicitly defined `PartialOrd` is a risky practice that may cause unexpected behavior.
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=== Code examples
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==== Noncompliant code example
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[source,rust,diff-id=1,diff-type=noncompliant]
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----
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#[derive(Ord, PartialEq, Eq)]
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struct Foo;
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impl PartialOrd for Foo {
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fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
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None // Noncompliant: Manually implemented PartialOrd when Ord is derived.
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}
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}
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----
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==== Compliant solution
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[source,rust,diff-id=1,diff-type=compliant]
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----
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#[derive(PartialEq, Eq)]
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struct Foo;
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impl PartialOrd for Foo {
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fn partial_cmp(&self, other: &Foo) -> Option<Ordering> {
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Some(self.cmp(other)) // Compliant: Manual implementation is consistent with Ord.
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}
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}
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impl Ord for Foo {
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fn cmp(&self, other: &Foo) -> Ordering {
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// Implementation here
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}
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}
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----
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Or, if a custom ordering is not needed:
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[source,rust,diff-id=1,diff-type=compliant]
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----
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#[derive(Ord, PartialOrd, PartialEq, Eq)]
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struct Foo; // Compliant: Both Ord and PartialOrd are derived.
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----
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== Resources
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=== Documentation
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* Clippy Lints - https://rust-lang.github.io/rust-clippy/master/index.html#derive_ord_xor_partial_ord
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