# [−] [src] Struct rand_core::block::BlockRng

    pub struct BlockRng<R: BlockRngCore + ?Sized> {
        pub core: R,
        // some fields omitted
    }

A wrapper type implementing [`RngCore`] for some type implementing [`BlockRngCore`] with `u32` array buffer; i.e. this can be used to implement a full RNG from just a `generate` function.

The `core` field may be accessed directly but the results buffer may not. PRNG implementations can simply use a type alias (`pub type MyRng = BlockRng<MyRngCore>;`) but might prefer to use a wrapper type (`pub struct MyRng(BlockRng<MyRngCore>);`); the latter must re-implement `RngCore` but hides the implementation details and allows extra functionality to be defined on the RNG (e.g. `impl MyRng { fn set_stream(...){...} }`).

`BlockRng` has heavily optimized implementations of the [`RngCore`] methods reading values from the results buffer, as well as calling [`BlockRngCore::generate`] directly on the output array when `fill_bytes` / `try_fill_bytes` is called on a large array. These methods also handle the bookkeeping of when to generate a new batch of values.

No whole generated `u32` values are thown away and all values are consumed in-order. `next_u32` simply takes the next available `u32` value. `next_u64` is implemented by combining two `u32` values, least significant first. `fill_bytes` and `try_fill_bytes` consume a whole number of `u32` values, converting each `u32` to a byte slice in little-endian order. If the requested byte length is not a multiple of 4, some bytes will be discarded.

See also [`BlockRng64`] which uses `u64` array buffers. Currently there is no direct support for other buffer types.

For easy initialization `BlockRng` also implements [`SeedableRng`].

## Fields

`core: R`

The core part of the RNG, implementing the `generate` function.

## Methods

### `impl<R: BlockRngCore> BlockRng<R>` [src]

#### `pub fn new(core: R) -> BlockRng<R>` [src]

Create a new `BlockRng` from an existing RNG implementing `BlockRngCore`. Results will be generated on first use.

#### `pub fn index(&self) -> usize` [src]

Get the index into the result buffer.

If this is equal to or larger than the size of the result buffer then the buffer is "empty" and `generate()` must be called to produce new results.

#### `pub fn reset(&mut self)` [src]

Reset the number of available results. This will force a new set of results to be generated on next use.

#### `pub fn generate_and_set(&mut self, index: usize)` [src]

Generate a new set of results immediately, setting the index to the given value.

## Trait Implementations

### `impl<R: BlockRngCore<Item = u32>> RngCore for BlockRng<R> where
<R as BlockRngCore>::Results: AsRef<[u32]> + AsMut<[u32]>,` [src]

#### `fn next_u32(&mut self) -> u32` [src]

Return the next random `u32`. Read more

#### `fn next_u64(&mut self) -> u64` [src]

Return the next random `u64`. Read more

#### `fn fill_bytes(&mut self, dest: &mut [u8])` [src]

Fill `dest` with random data. Read more

#### `fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error>` [src]

Fill `dest` entirely with random data. Read more

### `impl<R: BlockRngCore + CryptoRng> CryptoRng for BlockRng<R>` [src]

### `impl<R: BlockRngCore + SeedableRng> SeedableRng for BlockRng<R>` [src]

#### `type Seed = R::Seed`

Seed type, which is restricted to types mutably-dereferencable as `u8` arrays (we recommend `[u8; N]` for some `N`). Read more

#### `fn from_seed(seed: Self::Seed) -> Self` [src]

Create a new PRNG using the given seed. Read more

#### `fn seed_from_u64(seed: u64) -> Self` [src]

Create a new PRNG using a `u64` seed. Read more

#### `fn from_rng<S: RngCore>(rng: S) -> Result<Self, Error>` [src]

Create a new PRNG seeded from another `Rng`. Read more

#### `fn from_entropy() -> Self` [src]

Creates a new instance of the RNG seeded via [`getrandom`]. Read more

### `impl<R: Clone + BlockRngCore + ?Sized> Clone for BlockRng<R> where
R::Results: Clone,` [src]

#### `fn clone(&self) -> BlockRng<R>` [src]

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, source: &Self)`1.0.0 [src]

Performs copy-assignment from `source`. Read more

### `impl<R: BlockRngCore + Debug> Debug for BlockRng<R>` [src]

#### `fn fmt(&self, fmt: &mut Formatter) -> Result` [src]

Formats the value using the given formatter. Read more

## Auto Trait Implementations

### `impl<R: ?Sized> Send for BlockRng<R> where
R: Send,
<R as BlockRngCore>::Results: Send,`

### `impl<R: ?Sized> Sync for BlockRng<R> where
R: Sync,
<R as BlockRngCore>::Results: Sync,`

## Blanket Implementations

### `impl<T> From<T> for T` [src]

#### `fn from(t: T) -> T` [src]

Performs the conversion.

### `impl<T> ToOwned for T where
T: Clone,` [src]

#### `type Owned = T`

The resulting type after obtaining ownership.

#### `fn to_owned(&self) -> T` [src]

Creates owned data from borrowed data, usually by cloning. Read more

#### `fn clone_into(&self, target: &mut T)` [src]

🔬 This is a nightly-only experimental API. (`toowned_clone_into`)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

### `impl<T, U> Into<U> for T where
U: From<T>,` [src]

#### `fn into(self) -> U` [src]

Performs the conversion.

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

#### `fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>` [src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

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

The type returned in the event of a conversion error.

#### `fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>` [src]

Performs the conversion.

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

#### `fn borrow_mut(&mut self) -> &mut T` [src]

Mutably borrows from an owned value. Read more

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `fn borrow(&self) -> &T` [src]

Immutably borrows from an owned value. Read more

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `fn type_id(&self) -> TypeId` [src]

Gets the `TypeId` of `self`. Read more

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