# Struct std::hash::BuildHasherDefault

1.7.0 · source ·

    pub struct BuildHasherDefault<H>(/* private fields */);

Expand description

Used to create a default `BuildHasher` instance for types that implement `Hasher` and `Default`.

`BuildHasherDefault<H>` can be used when a type `H` implements `Hasher` and `Default`, and you need a corresponding `BuildHasher` instance, but none is defined.

Any `BuildHasherDefault` is zero-sized. It can be created with `default`. When using `BuildHasherDefault` with `HashMap` or `HashSet`, this doesn’t need to be done, since they implement appropriate `Default` instances themselves.

## Examples

Using `BuildHasherDefault` to specify a custom `BuildHasher` for `HashMap`:

    use std::collections::HashMap;
    use std::hash::{BuildHasherDefault, Hasher};

    #[derive(Default)]
    struct MyHasher;

    impl Hasher for MyHasher {
        fn write(&mut self, bytes: &[u8]) {
            // Your hashing algorithm goes here!
           unimplemented!()
        }

        fn finish(&self) -> u64 {
            // Your hashing algorithm goes here!
            unimplemented!()
        }
    }

    type MyBuildHasher = BuildHasherDefault<MyHasher>;

    let hash_map = HashMap::<u32, u32, MyBuildHasher>::default();

Run

## Trait Implementations§

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### impl<H> BuildHasher for BuildHasherDefault<H>where H: Default + Hasher,

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#### type Hasher = H

Type of the hasher that will be created.
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#### fn build_hasher(&self) -> H

Creates a new hasher. Read more
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### impl<H> Clone for BuildHasherDefault<H>

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#### fn clone(&self) -> BuildHasherDefault<H>

Returns a copy of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl<H> Debug for BuildHasherDefault<H>

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
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### impl<H> Default for BuildHasherDefault<H>

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#### fn default() -> BuildHasherDefault<H>

Returns the “default value” for a type. Read more
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### impl<H> PartialEq for BuildHasherDefault<H>

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#### fn eq(&self, _other: &BuildHasherDefault<H>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Rhs) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
1.29.0 · source§

### impl<H> Eq for BuildHasherDefault<H>

## Auto Trait Implementations§

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### impl<H> RefUnwindSafe for BuildHasherDefault<H>

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### impl<H> Send for BuildHasherDefault<H>

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### impl<H> Sync for BuildHasherDefault<H>

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### impl<H> Unpin for BuildHasherDefault<H>

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### impl<H> UnwindSafe for BuildHasherDefault<H>

## Blanket Implementations§

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### impl<T> Any for Twhere T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for Twhere T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for Twhere T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for Twhere U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T> ToOwned for Twhere T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.