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    // We *mostly* avoid unsafe code, but `map::core::raw` allows it to use `RawTable` buckets.
    #![deny(unsafe_code)]
    #![warn(rust_2018_idioms)]
    #![doc(html_root_url = "https://docs.rs/indexmap/1/")]
    #![no_std]

    //! [`IndexMap`] is a hash table where the iteration order of the key-value
    //! pairs is independent of the hash values of the keys.
    //!
    //! [`IndexSet`] is a corresponding hash set using the same implementation and
    //! with similar properties.
    //!
    //! [`IndexMap`]: map/struct.IndexMap.html
    //! [`IndexSet`]: set/struct.IndexSet.html
    //!
    //!
    //! ### Feature Highlights
    //!
    //! [`IndexMap`] and [`IndexSet`] are drop-in compatible with the std `HashMap`
    //! and `HashSet`, but they also have some features of note:
    //!
    //! - The ordering semantics (see their documentation for details)
    //! - Sorting methods and the [`.pop()`][IndexMap::pop] methods.
    //! - The [`Equivalent`] trait, which offers more flexible equality definitions
    //!   between borrowed and owned versions of keys.
    //! - The [`MutableKeys`][map::MutableKeys] trait, which gives opt-in mutable
    //!   access to hash map keys.
    //!
    //! ### Alternate Hashers
    //!
    //! [`IndexMap`] and [`IndexSet`] have a default hasher type `S = RandomState`,
    //! just like the standard `HashMap` and `HashSet`, which is resistant to
    //! HashDoS attacks but not the most performant. Type aliases can make it easier
    //! to use alternate hashers:
    //!
    //! ```
    //! use fnv::FnvBuildHasher;
    //! use fxhash::FxBuildHasher;
    //! use indexmap::{IndexMap, IndexSet};
    //!
    //! type FnvIndexMap<K, V> = IndexMap<K, V, FnvBuildHasher>;
    //! type FnvIndexSet<T> = IndexSet<T, FnvBuildHasher>;
    //!
    //! type FxIndexMap<K, V> = IndexMap<K, V, FxBuildHasher>;
    //! type FxIndexSet<T> = IndexSet<T, FxBuildHasher>;
    //!
    //! let std: IndexSet<i32> = (0..100).collect();
    //! let fnv: FnvIndexSet<i32> = (0..100).collect();
    //! let fx: FxIndexSet<i32> = (0..100).collect();
    //! assert_eq!(std, fnv);
    //! assert_eq!(std, fx);
    //! ```
    //!
    //! ### Rust Version
    //!
    //! This version of indexmap requires Rust 1.36 or later.
    //!
    //! The indexmap 1.x release series will use a carefully considered version
    //! upgrade policy, where in a later 1.x version, we will raise the minimum
    //! required Rust version.
    //!
    //! ## No Standard Library Targets
    //!
    //! This crate supports being built without `std`, requiring
    //! `alloc` instead. This is enabled automatically when it is detected that
    //! `std` is not available. There is no crate feature to enable/disable to
    //! trigger this. It can be tested by building for a std-less target.
    //!
    //! - Creating maps and sets using [`new`][IndexMap::new] and
    //! [`with_capacity`][IndexMap::with_capacity] is unavailable without `std`.
    //!   Use methods [`IndexMap::default`][def],
    //!   [`with_hasher`][IndexMap::with_hasher],
    //!   [`with_capacity_and_hasher`][IndexMap::with_capacity_and_hasher] instead.
    //!   A no-std compatible hasher will be needed as well, for example
    //!   from the crate `twox-hash`.
    //! - Macros [`indexmap!`] and [`indexset!`] are unavailable without `std`.
    //!
    //! [def]: map/struct.IndexMap.html#impl-Default

    #[cfg(not(has_std))]
    extern crate alloc;

    #[cfg(has_std)]
    #[macro_use]
    extern crate std;

    #[cfg(not(has_std))]
    use alloc::vec::{self, Vec};

    #[cfg(has_std)]
    use std::vec::{self, Vec};

    #[macro_use]
    mod macros;
    mod equivalent;
    mod mutable_keys;
    #[cfg(feature = "serde")]
    mod serde;
    #[cfg(feature = "serde")]
    pub mod serde_seq;
    mod util;

    pub mod map;
    pub mod set;

    // Placed after `map` and `set` so new `rayon` methods on the types
    // are documented after the "normal" methods.
    #[cfg(feature = "rayon")]
    mod rayon;

    pub use crate::equivalent::Equivalent;
    pub use crate::map::IndexMap;
    pub use crate::set::IndexSet;

    // shared private items

    /// Hash value newtype. Not larger than usize, since anything larger
    /// isn't used for selecting position anyway.
    #[derive(Clone, Copy, Debug, PartialEq)]
    struct HashValue(usize);

    impl HashValue {
        #[inline(always)]
        fn get(self) -> u64 {
            self.0 as u64
        }
    }

    #[derive(Copy, Debug)]
    struct Bucket<K, V> {
        hash: HashValue,
        key: K,
        value: V,
    }

    impl<K, V> Clone for Bucket<K, V>
    where
        K: Clone,
        V: Clone,
    {
        fn clone(&self) -> Self {
            Bucket {
                hash: self.hash,
                key: self.key.clone(),
                value: self.value.clone(),
            }
        }

        fn clone_from(&mut self, other: &Self) {
            self.hash = other.hash;
            self.key.clone_from(&other.key);
            self.value.clone_from(&other.value);
        }
    }

    impl<K, V> Bucket<K, V> {
        // field accessors -- used for `f` instead of closures in `.map(f)`
        fn key_ref(&self) -> &K {
            &self.key
        }
        fn value_ref(&self) -> &V {
            &self.value
        }
        fn value_mut(&mut self) -> &mut V {
            &mut self.value
        }
        fn key(self) -> K {
            self.key
        }
        fn key_value(self) -> (K, V) {
            (self.key, self.value)
        }
        fn refs(&self) -> (&K, &V) {
            (&self.key, &self.value)
        }
        fn ref_mut(&mut self) -> (&K, &mut V) {
            (&self.key, &mut self.value)
        }
        fn muts(&mut self) -> (&mut K, &mut V) {
            (&mut self.key, &mut self.value)
        }
    }

    trait Entries {
        type Entry;
        fn into_entries(self) -> Vec<Self::Entry>;
        fn as_entries(&self) -> &[Self::Entry];
        fn as_entries_mut(&mut self) -> &mut [Self::Entry];
        fn with_entries<F>(&mut self, f: F)
        where
            F: FnOnce(&mut [Self::Entry]);
    }