Struct Lazy 

pub struct Lazy<T: Read> { /* private fields */ }

A type which can be deserialized lazily.

This is useful when deserializing a value is expensive, and you don’t want to immediately pay this cost. This type allows you to move this cost to a later point in your program, or use parallelism to spread the cost across computing cores.

Usage

Any usage of the type requires that T implements Read, because we need to know what type Read::Cfg is.

Construction

If you have a T, you can use Lazy::new:

let l = Lazy::new(4000u64);

or Into:

let l: Lazy<u64> = 4000u64.into();

If you don’t have a T, then you can instead create a Lazy using bytes and a Read::Cfg:

let l: Lazy<u64> = Lazy::deferred(&mut 4000u64.encode(), ());

Consumption

Given a Lazy, use Lazy::get to access the value:

let l = Lazy::<u64>::deferred(&mut 4000u64.encode(), ());
assert_eq!(l.get(), Some(&4000u64));
// Does not pay the cost of deserializing again
assert_eq!(l.get(), Some(&4000u64));

This returns an Option, because deserialization might fail.

Traits

Lazy can be serialized and deserialized, implementing Read, Write, and EncodeSize, based on the underlying implementation of T.

Furthermore, we implement Eq, Ord, Hash based on the implementation of T as well. These methods will force deserialization of the value.

Implementations

impl<T: Read> Lazy<T>

pub fn new(value: T) -> Self

Create a Lazy using a value.

pub fn deferred(buf: &mut impl Buf, cfg: T::Cfg) -> Self

Create a Lazy by deferring decoding of an underlying value.

The only cost incurred when this function is called is that of copying some bytes.

Use Self::get to access the actual value, by decoding these bytes.

impl<T: Read> Lazy<T>

pub fn get(&self) -> Option<&T>

Force decoding of the underlying value.

This will return None only if decoding the value fails.

This function wil incur the cost of decoding the value only once, so there’s no need to cache its output.

Trait Implementations

impl<T: Clone + Read> Clone for Lazy<T>

fn clone(&self) -> Lazy<T>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Read + Debug> Debug for Lazy<T>

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

Formats the value using the given formatter.

impl<T: Read + EncodeSize> EncodeSize for Lazy<T>

fn encode_size(&self) -> usize

Returns the encoded size of this value (in bytes).

fn encode_inline_size(&self) -> usize

Returns the encoded size excluding bytes passed to BufsMut::push during Write::write_bufs. Used to size the working buffer for inline writes. Override alongside Write::write_bufs for types where large Bytes fields go via push; failing to do so will over-allocate.

impl<T: Read + Encode> From<T> for Lazy<T>

fn from(value: T) -> Self

Converts to this type from the input type.

impl<T: Read + Hash> Hash for Lazy<T>

fn hash<H: Hasher>(&self, state: &mut H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<T: Read + Ord> Ord for Lazy<T>

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl<T: Read + PartialEq> PartialEq for Lazy<T>

fn eq(&self, other: &Self) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T: Read + PartialOrd> PartialOrd for Lazy<T>

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

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

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl<T: Read + FixedSize> Read for Lazy<T>

type Cfg = <T as Read>::Cfg

The Cfg type parameter allows passing configuration during the read process. This is crucial for safely decoding untrusted data, for example, by providing size limits for collections or strings.

fn read_cfg(buf: &mut impl Buf, cfg: &Self::Cfg) -> Result<Self, Error>

Reads a value from the buffer using the provided configuration cfg.

impl<T: Read + Write> Write for Lazy<T>

fn write(&self, buf: &mut impl BufMut)

Writes the binary representation of self to the provided buffer buf.

fn write_bufs(&self, buf: &mut impl BufsMut)

Writes to a BufsMut, allowing existing Bytes chunks to be appended via BufsMut::push instead of written inline. Must encode to the same format as Write::write. Defaults to Write::write.

impl<T: Read + Eq> Eq for Lazy<T>