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use crate::*;
use core::fmt;
/// A map-like [`Valuable`] sub-type.
///
/// Implemented by [`Valuable`] types that have a map-like shape. This includes
/// [`HashMap`] and other Rust [collection] types. Values that implement
/// `Mappable` must return [`Value::Mappable`] from their [`Value::as_value`]
/// implementation.
///
/// [collection]: https://doc.rust-lang.org/stable/std/collections/index.html
///
/// # Inspecting
///
/// Inspecting `Mappable` entries is done by visiting the value. When visiting a
/// `Mappable`, contained entries are passed one-by-one to the visitor by
/// repeatedly calling [`visit_entry()`].
///
/// See [`Visit`] documentation for more details.
///
/// [`visit_entry()`]: Visit::visit_entry
/// [`HashMap`]: std::collections::HashMap
///
/// # Implementing
///
/// Implementing `Mappable` for a custom map type. The map is represented using
/// a `Vec` of key/value pairs.
///
/// ```
/// use valuable::{Mappable, Valuable, Value, Visit};
///
/// struct MyMap<K, V> {
/// entries: Vec<(K, V)>,
/// }
///
/// impl<K: Valuable, V: Valuable> Valuable for MyMap<K, V> {
/// fn as_value(&self) -> Value<'_> {
/// Value::Mappable(self)
/// }
///
/// fn visit(&self, visit: &mut dyn Visit) {
/// for (k, v) in &self.entries {
/// visit.visit_entry(k.as_value(), v.as_value());
/// }
/// }
/// }
///
/// impl<K: Valuable, V: Valuable> Mappable for MyMap<K, V> {
/// fn size_hint(&self) -> (usize, Option<usize>) {
/// let len = self.entries.len();
/// (len, Some(len))
/// }
/// }
/// ```
pub trait Mappable: Valuable {
/// Returns the bounds on the remaining length of the `Mappable`.
///
/// Specifically, `size_hint()` returns a tuple where the first element is
/// the lower bound, and the second element is the upper bound.
///
/// The second half of the tuple that is returned is an
/// [`Option`]`<`[`usize`]`>`. A [`None`] here means that either there is no
/// known upper bound, or the upper bound is larger than [`usize`].
///
/// # Implementation notes
///
/// It is not enforced that a `Mappable` implementation yields the declared
/// number of elements. A buggy implementation may yield less than the lower
/// bound or more than the upper bound of elements.
///
/// `size_hint()` is primarily intended to be used for optimizations such as
/// reserving space for the elements of the `Mappable`, but must not be
/// trusted to e.g., omit bounds checks in unsafe code. An incorrect
/// implementation of `size_hint()` should not lead to memory safety
/// violations.
///
/// That said, the implementation should provide a correct estimation,
/// because otherwise it would be a violation of the trait's protocol.
///
/// [`usize`]: type@usize
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// use valuable::Mappable;
/// use std::collections::HashMap;
///
/// let mut map = HashMap::new();
/// map.insert("one", 1);
/// map.insert("two", 2);
/// map.insert("three", 3);
///
/// assert_eq!((3, Some(3)), map.size_hint());
/// ```
fn size_hint(&self) -> (usize, Option<usize>);
}
macro_rules! deref {
(
$(
$(#[$attrs:meta])*
$ty:ty,
)*
) => {
$(
$(#[$attrs])*
impl<T: ?Sized + Mappable> Mappable for $ty {
fn size_hint(&self) -> (usize, Option<usize>) {
T::size_hint(&**self)
}
}
)*
};
}
deref! {
&T,
&mut T,
#[cfg(feature = "alloc")]
alloc::boxed::Box<T>,
#[cfg(feature = "alloc")]
alloc::rc::Rc<T>,
#[cfg(not(valuable_no_atomic_cas))]
#[cfg(feature = "alloc")]
alloc::sync::Arc<T>,
}
#[cfg(feature = "std")]
impl<K: Valuable, V: Valuable> Valuable for std::collections::HashMap<K, V> {
fn as_value(&self) -> Value<'_> {
Value::Mappable(self)
}
fn visit(&self, visit: &mut dyn Visit) {
for (key, value) in self.iter() {
visit.visit_entry(key.as_value(), value.as_value());
}
}
}
#[cfg(feature = "std")]
impl<K: Valuable, V: Valuable> Mappable for std::collections::HashMap<K, V> {
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter().size_hint()
}
}
#[cfg(feature = "alloc")]
impl<K: Valuable, V: Valuable> Valuable for alloc::collections::BTreeMap<K, V> {
fn as_value(&self) -> Value<'_> {
Value::Mappable(self)
}
fn visit(&self, visit: &mut dyn Visit) {
for (key, value) in self.iter() {
visit.visit_entry(key.as_value(), value.as_value());
}
}
}
#[cfg(feature = "alloc")]
impl<K: Valuable, V: Valuable> Mappable for alloc::collections::BTreeMap<K, V> {
fn size_hint(&self) -> (usize, Option<usize>) {
self.iter().size_hint()
}
}
impl fmt::Debug for dyn Mappable + '_ {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
struct DebugMappable<'a, 'b> {
fmt: fmt::DebugMap<'a, 'b>,
}
impl Visit for DebugMappable<'_, '_> {
fn visit_entry(&mut self, key: Value<'_>, value: Value<'_>) {
self.fmt.entry(&key, &value);
}
fn visit_value(&mut self, _: Value<'_>) {}
}
let mut debug = DebugMappable {
fmt: fmt.debug_map(),
};
self.visit(&mut debug);
debug.fmt.finish()
}
}