Struct sp_storage::PrefixedStorageKey[][src]

#[repr(transparent)]
pub struct PrefixedStorageKey(_);
Expand description

Storage key of a child trie, it contains the prefix to the key.

Implementations

Create a prefixed storage key from its byte array representation.

Create a prefixed storage key reference.

Get inner key, this should only be needed when writing into parent trie to avoid an allocation.

Methods from Deref<Target = Vec<u8>>

Returns the number of elements the vector can hold without reallocating.

Examples

let vec: Vec<i32> = Vec::with_capacity(10);
assert_eq!(vec.capacity(), 10);

Reserves capacity for at least additional more elements to be inserted in the given Vec<T>. The collection may reserve more space to avoid frequent reallocations. After calling reserve, capacity will be greater than or equal to self.len() + additional. Does nothing if capacity is already sufficient.

Panics

Panics if the new capacity exceeds isize::MAX bytes.

Examples

let mut vec = vec![1];
vec.reserve(10);
assert!(vec.capacity() >= 11);

Reserves the minimum capacity for exactly additional more elements to be inserted in the given Vec<T>. After calling reserve_exact, capacity will be greater than or equal to self.len() + additional. Does nothing if the capacity is already sufficient.

Note that the allocator may give the collection more space than it requests. Therefore, capacity can not be relied upon to be precisely minimal. Prefer reserve if future insertions are expected.

Panics

Panics if the new capacity overflows usize.

Examples

let mut vec = vec![1];
vec.reserve_exact(10);
assert!(vec.capacity() >= 11);
🔬 This is a nightly-only experimental API. (try_reserve)

new API

Tries to reserve capacity for at least additional more elements to be inserted in the given Vec<T>. The collection may reserve more space to avoid frequent reallocations. After calling try_reserve, capacity will be greater than or equal to self.len() + additional. Does nothing if capacity is already sufficient.

Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

Examples

#![feature(try_reserve)]
use std::collections::TryReserveError;

fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
    let mut output = Vec::new();

    // Pre-reserve the memory, exiting if we can't
    output.try_reserve(data.len())?;

    // Now we know this can't OOM in the middle of our complex work
    output.extend(data.iter().map(|&val| {
        val * 2 + 5 // very complicated
    }));

    Ok(output)
}
🔬 This is a nightly-only experimental API. (try_reserve)

new API

Tries to reserve the minimum capacity for exactly additional elements to be inserted in the given Vec<T>. After calling try_reserve_exact, capacity will be greater than or equal to self.len() + additional if it returns Ok(()). Does nothing if the capacity is already sufficient.

Note that the allocator may give the collection more space than it requests. Therefore, capacity can not be relied upon to be precisely minimal. Prefer reserve if future insertions are expected.

Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

Examples

#![feature(try_reserve)]
use std::collections::TryReserveError;

fn process_data(data: &[u32]) -> Result<Vec<u32>, TryReserveError> {
    let mut output = Vec::new();

    // Pre-reserve the memory, exiting if we can't
    output.try_reserve_exact(data.len())?;

    // Now we know this can't OOM in the middle of our complex work
    output.extend(data.iter().map(|&val| {
        val * 2 + 5 // very complicated
    }));

    Ok(output)
}

Shrinks the capacity of the vector as much as possible.

It will drop down as close as possible to the length but the allocator may still inform the vector that there is space for a few more elements.

Examples

let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3]);
assert_eq!(vec.capacity(), 10);
vec.shrink_to_fit();
assert!(vec.capacity() >= 3);

Shrinks the capacity of the vector with a lower bound.

The capacity will remain at least as large as both the length and the supplied value.

If the current capacity is less than the lower limit, this is a no-op.

Examples

let mut vec = Vec::with_capacity(10);
vec.extend([1, 2, 3]);
assert_eq!(vec.capacity(), 10);
vec.shrink_to(4);
assert!(vec.capacity() >= 4);
vec.shrink_to(0);
assert!(vec.capacity() >= 3);

Shortens the vector, keeping the first len elements and dropping the rest.

If len is greater than the vector’s current length, this has no effect.

The drain method can emulate truncate, but causes the excess elements to be returned instead of dropped.

Note that this method has no effect on the allocated capacity of the vector.

Examples

Truncating a five element vector to two elements:

let mut vec = vec![1, 2, 3, 4, 5];
vec.truncate(2);
assert_eq!(vec, [1, 2]);

No truncation occurs when len is greater than the vector’s current length:

let mut vec = vec![1, 2, 3];
vec.truncate(8);
assert_eq!(vec, [1, 2, 3]);

Truncating when len == 0 is equivalent to calling the clear method.

let mut vec = vec![1, 2, 3];
vec.truncate(0);
assert_eq!(vec, []);

Extracts a slice containing the entire vector.

Equivalent to &s[..].

Examples

use std::io::{self, Write};
let buffer = vec![1, 2, 3, 5, 8];
io::sink().write(buffer.as_slice()).unwrap();

Extracts a mutable slice of the entire vector.

Equivalent to &mut s[..].

Examples

use std::io::{self, Read};
let mut buffer = vec![0; 3];
io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();

Returns a raw pointer to the vector’s buffer.

The caller must ensure that the vector outlives the pointer this function returns, or else it will end up pointing to garbage. Modifying the vector may cause its buffer to be reallocated, which would also make any pointers to it invalid.

The caller must also ensure that the memory the pointer (non-transitively) points to is never written to (except inside an UnsafeCell) using this pointer or any pointer derived from it. If you need to mutate the contents of the slice, use as_mut_ptr.

Examples

let x = vec![1, 2, 4];
let x_ptr = x.as_ptr();

unsafe {
    for i in 0..x.len() {
        assert_eq!(*x_ptr.add(i), 1 << i);
    }
}

Returns an unsafe mutable pointer to the vector’s buffer.

The caller must ensure that the vector outlives the pointer this function returns, or else it will end up pointing to garbage. Modifying the vector may cause its buffer to be reallocated, which would also make any pointers to it invalid.

Examples

// Allocate vector big enough for 4 elements.
let size = 4;
let mut x: Vec<i32> = Vec::with_capacity(size);
let x_ptr = x.as_mut_ptr();

// Initialize elements via raw pointer writes, then set length.
unsafe {
    for i in 0..size {
        *x_ptr.add(i) = i as i32;
    }
    x.set_len(size);
}
assert_eq!(&*x, &[0, 1, 2, 3]);
🔬 This is a nightly-only experimental API. (allocator_api)

Returns a reference to the underlying allocator.

Forces the length of the vector to new_len.

This is a low-level operation that maintains none of the normal invariants of the type. Normally changing the length of a vector is done using one of the safe operations instead, such as truncate, resize, extend, or clear.

Safety

  • new_len must be less than or equal to capacity().
  • The elements at old_len..new_len must be initialized.

Examples

This method can be useful for situations in which the vector is serving as a buffer for other code, particularly over FFI:

pub fn get_dictionary(&self) -> Option<Vec<u8>> {
    // Per the FFI method's docs, "32768 bytes is always enough".
    let mut dict = Vec::with_capacity(32_768);
    let mut dict_length = 0;
    // SAFETY: When `deflateGetDictionary` returns `Z_OK`, it holds that:
    // 1. `dict_length` elements were initialized.
    // 2. `dict_length` <= the capacity (32_768)
    // which makes `set_len` safe to call.
    unsafe {
        // Make the FFI call...
        let r = deflateGetDictionary(self.strm, dict.as_mut_ptr(), &mut dict_length);
        if r == Z_OK {
            // ...and update the length to what was initialized.
            dict.set_len(dict_length);
            Some(dict)
        } else {
            None
        }
    }
}

While the following example is sound, there is a memory leak since the inner vectors were not freed prior to the set_len call:

let mut vec = vec![vec![1, 0, 0],
                   vec![0, 1, 0],
                   vec![0, 0, 1]];
// SAFETY:
// 1. `old_len..0` is empty so no elements need to be initialized.
// 2. `0 <= capacity` always holds whatever `capacity` is.
unsafe {
    vec.set_len(0);
}

Normally, here, one would use clear instead to correctly drop the contents and thus not leak memory.

Removes an element from the vector and returns it.

The removed element is replaced by the last element of the vector.

This does not preserve ordering, but is O(1).

Panics

Panics if index is out of bounds.

Examples

let mut v = vec!["foo", "bar", "baz", "qux"];

assert_eq!(v.swap_remove(1), "bar");
assert_eq!(v, ["foo", "qux", "baz"]);

assert_eq!(v.swap_remove(0), "foo");
assert_eq!(v, ["baz", "qux"]);

Inserts an element at position index within the vector, shifting all elements after it to the right.

Panics

Panics if index > len.

Examples

let mut vec = vec![1, 2, 3];
vec.insert(1, 4);
assert_eq!(vec, [1, 4, 2, 3]);
vec.insert(4, 5);
assert_eq!(vec, [1, 4, 2, 3, 5]);

Removes and returns the element at position index within the vector, shifting all elements after it to the left.

Note: Because this shifts over the remaining elements, it has a worst-case performance of O(n). If you don’t need the order of elements to be preserved, use swap_remove instead.

Panics

Panics if index is out of bounds.

Examples

let mut v = vec![1, 2, 3];
assert_eq!(v.remove(1), 2);
assert_eq!(v, [1, 3]);

Retains only the elements specified by the predicate.

In other words, remove all elements e such that f(&e) returns false. This method operates in place, visiting each element exactly once in the original order, and preserves the order of the retained elements.

Examples

let mut vec = vec![1, 2, 3, 4];
vec.retain(|&x| x % 2 == 0);
assert_eq!(vec, [2, 4]);

Because the elements are visited exactly once in the original order, external state may be used to decide which elements to keep.

let mut vec = vec![1, 2, 3, 4, 5];
let keep = [false, true, true, false, true];
let mut iter = keep.iter();
vec.retain(|_| *iter.next().unwrap());
assert_eq!(vec, [2, 3, 5]);

Removes all but the first of consecutive elements in the vector that resolve to the same key.

If the vector is sorted, this removes all duplicates.

Examples

let mut vec = vec![10, 20, 21, 30, 20];

vec.dedup_by_key(|i| *i / 10);

assert_eq!(vec, [10, 20, 30, 20]);

Removes all but the first of consecutive elements in the vector satisfying a given equality relation.

The same_bucket function is passed references to two elements from the vector and must determine if the elements compare equal. The elements are passed in opposite order from their order in the slice, so if same_bucket(a, b) returns true, a is removed.

If the vector is sorted, this removes all duplicates.

Examples

let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];

vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));

assert_eq!(vec, ["foo", "bar", "baz", "bar"]);

Appends an element to the back of a collection.

Panics

Panics if the new capacity exceeds isize::MAX bytes.

Examples

let mut vec = vec![1, 2];
vec.push(3);
assert_eq!(vec, [1, 2, 3]);

Removes the last element from a vector and returns it, or None if it is empty.

Examples

let mut vec = vec![1, 2, 3];
assert_eq!(vec.pop(), Some(3));
assert_eq!(vec, [1, 2]);

Moves all the elements of other into Self, leaving other empty.

Panics

Panics if the number of elements in the vector overflows a usize.

Examples

let mut vec = vec![1, 2, 3];
let mut vec2 = vec![4, 5, 6];
vec.append(&mut vec2);
assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
assert_eq!(vec2, []);

Creates a draining iterator that removes the specified range in the vector and yields the removed items.

When the iterator is dropped, all elements in the range are removed from the vector, even if the iterator was not fully consumed. If the iterator is not dropped (with mem::forget for example), it is unspecified how many elements are removed.

Panics

Panics if the starting point is greater than the end point or if the end point is greater than the length of the vector.

Examples

let mut v = vec![1, 2, 3];
let u: Vec<_> = v.drain(1..).collect();
assert_eq!(v, &[1]);
assert_eq!(u, &[2, 3]);

// A full range clears the vector
v.drain(..);
assert_eq!(v, &[]);

Clears the vector, removing all values.

Note that this method has no effect on the allocated capacity of the vector.

Examples

let mut v = vec![1, 2, 3];

v.clear();

assert!(v.is_empty());

Returns the number of elements in the vector, also referred to as its ‘length’.

Examples

let a = vec![1, 2, 3];
assert_eq!(a.len(), 3);

Returns true if the vector contains no elements.

Examples

let mut v = Vec::new();
assert!(v.is_empty());

v.push(1);
assert!(!v.is_empty());

Splits the collection into two at the given index.

Returns a newly allocated vector containing the elements in the range [at, len). After the call, the original vector will be left containing the elements [0, at) with its previous capacity unchanged.

Panics

Panics if at > len.

Examples

let mut vec = vec![1, 2, 3];
let vec2 = vec.split_off(1);
assert_eq!(vec, [1]);
assert_eq!(vec2, [2, 3]);

Resizes the Vec in-place so that len is equal to new_len.

If new_len is greater than len, the Vec is extended by the difference, with each additional slot filled with the result of calling the closure f. The return values from f will end up in the Vec in the order they have been generated.

If new_len is less than len, the Vec is simply truncated.

This method uses a closure to create new values on every push. If you’d rather Clone a given value, use Vec::resize. If you want to use the Default trait to generate values, you can pass Default::default as the second argument.

Examples

let mut vec = vec![1, 2, 3];
vec.resize_with(5, Default::default);
assert_eq!(vec, [1, 2, 3, 0, 0]);

let mut vec = vec![];
let mut p = 1;
vec.resize_with(4, || { p *= 2; p });
assert_eq!(vec, [2, 4, 8, 16]);
🔬 This is a nightly-only experimental API. (vec_spare_capacity)

Returns the remaining spare capacity of the vector as a slice of MaybeUninit<T>.

The returned slice can be used to fill the vector with data (e.g. by reading from a file) before marking the data as initialized using the set_len method.

Examples

#![feature(vec_spare_capacity, maybe_uninit_extra)]

// Allocate vector big enough for 10 elements.
let mut v = Vec::with_capacity(10);

// Fill in the first 3 elements.
let uninit = v.spare_capacity_mut();
uninit[0].write(0);
uninit[1].write(1);
uninit[2].write(2);

// Mark the first 3 elements of the vector as being initialized.
unsafe {
    v.set_len(3);
}

assert_eq!(&v, &[0, 1, 2]);
🔬 This is a nightly-only experimental API. (vec_split_at_spare)

Returns vector content as a slice of T, along with the remaining spare capacity of the vector as a slice of MaybeUninit<T>.

The returned spare capacity slice can be used to fill the vector with data (e.g. by reading from a file) before marking the data as initialized using the set_len method.

Note that this is a low-level API, which should be used with care for optimization purposes. If you need to append data to a Vec you can use push, extend, extend_from_slice, extend_from_within, insert, append, resize or resize_with, depending on your exact needs.

Examples

#![feature(vec_split_at_spare, maybe_uninit_extra)]

let mut v = vec![1, 1, 2];

// Reserve additional space big enough for 10 elements.
v.reserve(10);

let (init, uninit) = v.split_at_spare_mut();
let sum = init.iter().copied().sum::<u32>();

// Fill in the next 4 elements.
uninit[0].write(sum);
uninit[1].write(sum * 2);
uninit[2].write(sum * 3);
uninit[3].write(sum * 4);

// Mark the 4 elements of the vector as being initialized.
unsafe {
    let len = v.len();
    v.set_len(len + 4);
}

assert_eq!(&v, &[1, 1, 2, 4, 8, 12, 16]);

Resizes the Vec in-place so that len is equal to new_len.

If new_len is greater than len, the Vec is extended by the difference, with each additional slot filled with value. If new_len is less than len, the Vec is simply truncated.

This method requires T to implement Clone, in order to be able to clone the passed value. If you need more flexibility (or want to rely on Default instead of Clone), use Vec::resize_with.

Examples

let mut vec = vec!["hello"];
vec.resize(3, "world");
assert_eq!(vec, ["hello", "world", "world"]);

let mut vec = vec![1, 2, 3, 4];
vec.resize(2, 0);
assert_eq!(vec, [1, 2]);

Clones and appends all elements in a slice to the Vec.

Iterates over the slice other, clones each element, and then appends it to this Vec. The other vector is traversed in-order.

Note that this function is same as extend except that it is specialized to work with slices instead. If and when Rust gets specialization this function will likely be deprecated (but still available).

Examples

let mut vec = vec![1];
vec.extend_from_slice(&[2, 3, 4]);
assert_eq!(vec, [1, 2, 3, 4]);

Copies elements from src range to the end of the vector.

Examples

let mut vec = vec![0, 1, 2, 3, 4];

vec.extend_from_within(2..);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4]);

vec.extend_from_within(..2);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1]);

vec.extend_from_within(4..8);
assert_eq!(vec, [0, 1, 2, 3, 4, 2, 3, 4, 0, 1, 4, 2, 3, 4]);

Removes consecutive repeated elements in the vector according to the PartialEq trait implementation.

If the vector is sorted, this removes all duplicates.

Examples

let mut vec = vec![1, 2, 2, 3, 2];

vec.dedup();

assert_eq!(vec, [1, 2, 3, 2]);

Creates a splicing iterator that replaces the specified range in the vector with the given replace_with iterator and yields the removed items. replace_with does not need to be the same length as range.

range is removed even if the iterator is not consumed until the end.

It is unspecified how many elements are removed from the vector if the Splice value is leaked.

The input iterator replace_with is only consumed when the Splice value is dropped.

This is optimal if:

  • The tail (elements in the vector after range) is empty,
  • or replace_with yields fewer or equal elements than range’s length
  • or the lower bound of its size_hint() is exact.

Otherwise, a temporary vector is allocated and the tail is moved twice.

Panics

Panics if the starting point is greater than the end point or if the end point is greater than the length of the vector.

Examples

let mut v = vec![1, 2, 3];
let new = [7, 8];
let u: Vec<_> = v.splice(..2, new).collect();
assert_eq!(v, &[7, 8, 3]);
assert_eq!(u, &[1, 2]);
🔬 This is a nightly-only experimental API. (drain_filter)

recently added

Creates an iterator which uses a closure to determine if an element should be removed.

If the closure returns true, then the element is removed and yielded. If the closure returns false, the element will remain in the vector and will not be yielded by the iterator.

Using this method is equivalent to the following code:

let mut i = 0;
while i < vec.len() {
    if some_predicate(&mut vec[i]) {
        let val = vec.remove(i);
        // your code here
    } else {
        i += 1;
    }
}

But drain_filter is easier to use. drain_filter is also more efficient, because it can backshift the elements of the array in bulk.

Note that drain_filter also lets you mutate every element in the filter closure, regardless of whether you choose to keep or remove it.

Examples

Splitting an array into evens and odds, reusing the original allocation:

#![feature(drain_filter)]
let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];

let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
let odds = numbers;

assert_eq!(evens, vec![2, 4, 6, 8, 14]);
assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);

Trait Implementations

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

The resulting type after dereferencing.

Dereferences the value.

Mutably dereferences the value.

Deserialize this value from the given Serde deserializer. Read more

Feeds this value into the given Hasher. Read more

Feeds a slice of this type into the given Hasher. Read more

This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

Restrict a value to a certain interval. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

Serialize this value into the given Serde serializer. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Performs the conversion.

Performs the conversion.

The resulting type after obtaining ownership.

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

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

recently added

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

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.