Struct Previous 

pub struct Previous<T: Clone + PartialEq + 'static> { /* private fields */ }

Tracks the previously observed value of some external reactive source.

Typical use: in a render closure, call previous.record(current) at the top, then read previous.get_previous().get() to find out what the value was on the previous render. The two reads are decoupled so callers can record and read independently.

Why a Signal<Option<T>>?

Because the very first call to record has no “previous” to report. The signal starts at None and flips to Some(value) after the first record. Render code can branch on the Option for “first render vs subsequent”.

Lombok caveat

Previous cannot use Lombok New because the previous: Signal<Option<T>> field would require T: Default to satisfy Signal::default(). The struct intentionally keeps T: Clone + PartialEq + 'static (no Default), and the constructor is hand-written in impl.rs to wrap the field with Signal::create(None).

Implementations

impl<T: Clone + PartialEq + 'static> Previous<T>

Inherent implementation of Previous.

pub fn new() -> Self

Creates a new Previous with no recorded value. The previous signal starts at None.

pub fn record(&self, current: T)

Records current as the new previous value. The next call to get_previous_snapshot() will return Some(current).

This is typically called at the top of a render closure so the signal stores the value just seen.

Arguments

• T: Clone + PartialEq + 'static - A generic type parameter.

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

Returns a snapshot of the previously recorded value, or None if no value has been recorded yet.

Returns

• Option<T> - The previous captured value, or None.

pub fn clear(&self)

Clears the recorded previous value, returning the tracker to the None state.

impl<T: Clone + PartialEq + 'static> Previous<T>

pub fn get_previous(&self) -> &Signal<Option<T>>

pub fn get_mut_previous(&mut self) -> &mut Signal<Option<T>>

pub fn set_previous(&mut self, val: Signal<Option<T>>) -> &mut Self

Trait Implementations

impl<T: Clone + Clone + PartialEq + 'static> Clone for Previous<T>

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

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T> Copy for Previous<T>

where T: Clone + PartialEq + 'static,

Previous<T> is Copy when T is — Signal<Option<T>> is already Copy (the signal registry hands out cheap usize addresses), so this blanket impl is sound.

impl<T: Debug + Clone + PartialEq + 'static> Debug for Previous<T>

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

Formats the value using the given formatter.

impl<T: Clone + PartialEq + 'static> Default for Previous<T>

Default-construction for Previous.

fn default() -> Self

Constructs a default Previous value.

impl<T: Clone + PartialEq + Debug + 'static> Display for Previous<T>

Debug formatting for Previous.

fn fmt(&self, formatter: &mut Formatter<'_>) -> FmtResult

Formats the Previous via the supplied formatter.

Arguments

• &mut Formatter<'_> - The formatter receiving the formatted output.

Returns

• FmtResult - Result of the formatting operation.