Trait rustc_data_structures::stable_hasher::StableOrd

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pub trait StableOrd: Ord {
    const CAN_USE_UNSTABLE_SORT: bool;
    const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: ();
}
Expand description

Trait for marking a type as having a sort order that is stable across compilation session boundaries. More formally:

Ord::cmp(a1, b1) == Ord::cmp(a2, b2)
   where a2 = decode(encode(a1, context1), context2)
         b2 = decode(encode(b1, context1), context2)

i.e. the result of Ord::cmp is not influenced by encoding the values in one session and then decoding them in another session.

This is trivially true for types where encoding and decoding don’t change the bytes of the values that are used during comparison and comparison only depends on these bytes (as opposed to some non-local state). Examples are u32, String, Path, etc.

But it is not true for:

  • *const T and *mut T because the values of these pointers will change between sessions.
  • DefIndex, CrateNum, LocalDefId, because their concrete values depend on state that might be different between compilation sessions.

The associated constant CAN_USE_UNSTABLE_SORT denotes whether unstable sorting can be used for this type. Set to true if and only if a == b implies a and b are fully indistinguishable.

Required Associated Constants§

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const CAN_USE_UNSTABLE_SORT: bool

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const THIS_IMPLEMENTATION_HAS_BEEN_TRIPLE_CHECKED: ()

Marker to ensure that implementors have carefully considered whether their Ord implementation obeys this trait’s contract.

Object Safety§

This trait is not object safe.

Implementations on Foreign Types§

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impl StableOrd for &str

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impl StableOrd for bool

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impl StableOrd for char

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impl StableOrd for i8

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impl StableOrd for i16

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impl StableOrd for i32

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impl StableOrd for i64

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impl StableOrd for i128

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impl StableOrd for isize

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impl StableOrd for u8

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impl StableOrd for u16

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impl StableOrd for u32

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impl StableOrd for u64

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impl StableOrd for u128

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impl StableOrd for ()

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impl StableOrd for usize

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impl StableOrd for String

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impl StableOrd for Path

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impl StableOrd for PathBuf

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impl<T1: StableOrd, T2: StableOrd> StableOrd for (T1, T2)

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impl<T1: StableOrd, T2: StableOrd, T3: StableOrd> StableOrd for (T1, T2, T3)

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impl<T1: StableOrd, T2: StableOrd, T3: StableOrd, T4: StableOrd> StableOrd for (T1, T2, T3, T4)

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impl<T: StableOrd> StableOrd for Option<T>

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impl<T: StableOrd> StableOrd for &T

Implementors§