//! Sources for key-values.
//!
//! This module defines the [`Source`] type and supporting APIs for
//! working with collections of key-values.
use crate::kv::{Error, Key, ToKey, ToValue, Value};
use std::fmt;
/// A source of key-values.
///
/// The source may be a single pair, a set of pairs, or a filter over a set of pairs.
/// Use the [`VisitSource`](trait.VisitSource.html) trait to inspect the structured data
/// in a source.
///
/// A source is like an iterator over its key-values, except with a push-based API
/// instead of a pull-based one.
///
/// # Examples
///
/// Enumerating the key-values in a source:
///
/// ```
/// # fn main() -> Result<(), log::kv::Error> {
/// use log::kv::{self, Source, Key, Value, VisitSource};
///
/// // A `VisitSource` that prints all key-values
/// // VisitSources are fed the key-value pairs of each key-values
/// struct Printer;
///
/// impl<'kvs> VisitSource<'kvs> for Printer {
/// fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), kv::Error> {
/// println!("{key}: {value}");
///
/// Ok(())
/// }
/// }
///
/// // A source with 3 key-values
/// // Common collection types implement the `Source` trait
/// let source = &[
/// ("a", 1),
/// ("b", 2),
/// ("c", 3),
/// ];
///
/// // Pass an instance of the `VisitSource` to a `Source` to visit it
/// source.visit(&mut Printer)?;
/// # Ok(())
/// # }
/// ```
pub trait Source {
/// Visit key-values.
///
/// A source doesn't have to guarantee any ordering or uniqueness of key-values.
/// If the given visitor returns an error then the source may early-return with it,
/// even if there are more key-values.
///
/// # Implementation notes
///
/// A source should yield the same key-values to a subsequent visitor unless
/// that visitor itself fails.
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error>;
/// Get the value for a given key.
///
/// If the key appears multiple times in the source then which key is returned
/// is implementation specific.
///
/// # Implementation notes
///
/// A source that can provide a more efficient implementation of this method
/// should override it.
fn get(&self, key: Key) -> Option<Value<'_>> {
get_default(self, key)
}
/// Count the number of key-values that can be visited.
///
/// # Implementation notes
///
/// A source that knows the number of key-values upfront may provide a more
/// efficient implementation.
///
/// A subsequent call to `visit` should yield the same number of key-values.
fn count(&self) -> usize {
count_default(self)
}
}
/// The default implementation of `Source::get`
fn get_default<'v>(source: &'v (impl Source + ?Sized), key: Key) -> Option<Value<'v>> {
struct Get<'k, 'v> {
key: Key<'k>,
found: Option<Value<'v>>,
}
impl<'k, 'kvs> VisitSource<'kvs> for Get<'k, 'kvs> {
fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
if self.key == key {
self.found = Some(value);
}
Ok(())
}
}
let mut get = Get { key, found: None };
let _ = source.visit(&mut get);
get.found
}
/// The default implementation of `Source::count`.
fn count_default(source: impl Source) -> usize {
struct Count(usize);
impl<'kvs> VisitSource<'kvs> for Count {
fn visit_pair(&mut self, _: Key<'kvs>, _: Value<'kvs>) -> Result<(), Error> {
self.0 += 1;
Ok(())
}
}
let mut count = Count(0);
let _ = source.visit(&mut count);
count.0
}
impl<'a, T> Source for &'a T
where
T: Source + ?Sized,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
Source::visit(&**self, visitor)
}
fn get(&self, key: Key) -> Option<Value<'_>> {
Source::get(&**self, key)
}
fn count(&self) -> usize {
Source::count(&**self)
}
}
impl<K, V> Source for (K, V)
where
K: ToKey,
V: ToValue,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
visitor.visit_pair(self.0.to_key(), self.1.to_value())
}
fn get(&self, key: Key) -> Option<Value<'_>> {
if self.0.to_key() == key {
Some(self.1.to_value())
} else {
None
}
}
fn count(&self) -> usize {
1
}
}
impl<S> Source for [S]
where
S: Source,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
for source in self {
source.visit(visitor)?;
}
Ok(())
}
fn get(&self, key: Key) -> Option<Value<'_>> {
for source in self {
if let Some(found) = source.get(key.clone()) {
return Some(found);
}
}
None
}
fn count(&self) -> usize {
self.iter().map(Source::count).sum()
}
}
impl<const N: usize, S> Source for [S; N]
where
S: Source,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
Source::visit(self as &[_], visitor)
}
fn get(&self, key: Key) -> Option<Value<'_>> {
Source::get(self as &[_], key)
}
fn count(&self) -> usize {
Source::count(self as &[_])
}
}
impl<S> Source for Option<S>
where
S: Source,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
if let Some(source) = self {
source.visit(visitor)?;
}
Ok(())
}
fn get(&self, key: Key) -> Option<Value<'_>> {
self.as_ref().and_then(|s| s.get(key))
}
fn count(&self) -> usize {
self.as_ref().map_or(0, Source::count)
}
}
/// A visitor for the key-value pairs in a [`Source`](trait.Source.html).
pub trait VisitSource<'kvs> {
/// Visit a key-value pair.
fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error>;
}
impl<'a, 'kvs, T> VisitSource<'kvs> for &'a mut T
where
T: VisitSource<'kvs> + ?Sized,
{
fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
(**self).visit_pair(key, value)
}
}
impl<'a, 'b: 'a, 'kvs> VisitSource<'kvs> for fmt::DebugMap<'a, 'b> {
fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
self.entry(&key, &value);
Ok(())
}
}
impl<'a, 'b: 'a, 'kvs> VisitSource<'kvs> for fmt::DebugList<'a, 'b> {
fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
self.entry(&(key, value));
Ok(())
}
}
impl<'a, 'b: 'a, 'kvs> VisitSource<'kvs> for fmt::DebugSet<'a, 'b> {
fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
self.entry(&(key, value));
Ok(())
}
}
impl<'a, 'b: 'a, 'kvs> VisitSource<'kvs> for fmt::DebugTuple<'a, 'b> {
fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
self.field(&key);
self.field(&value);
Ok(())
}
}
#[cfg(feature = "std")]
mod std_support {
use super::*;
use std::borrow::Borrow;
use std::collections::{BTreeMap, HashMap};
use std::hash::{BuildHasher, Hash};
use std::rc::Rc;
use std::sync::Arc;
impl<S> Source for Box<S>
where
S: Source + ?Sized,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
Source::visit(&**self, visitor)
}
fn get(&self, key: Key) -> Option<Value<'_>> {
Source::get(&**self, key)
}
fn count(&self) -> usize {
Source::count(&**self)
}
}
impl<S> Source for Arc<S>
where
S: Source + ?Sized,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
Source::visit(&**self, visitor)
}
fn get(&self, key: Key) -> Option<Value<'_>> {
Source::get(&**self, key)
}
fn count(&self) -> usize {
Source::count(&**self)
}
}
impl<S> Source for Rc<S>
where
S: Source + ?Sized,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
Source::visit(&**self, visitor)
}
fn get(&self, key: Key) -> Option<Value<'_>> {
Source::get(&**self, key)
}
fn count(&self) -> usize {
Source::count(&**self)
}
}
impl<S> Source for Vec<S>
where
S: Source,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
Source::visit(&**self, visitor)
}
fn get(&self, key: Key) -> Option<Value<'_>> {
Source::get(&**self, key)
}
fn count(&self) -> usize {
Source::count(&**self)
}
}
impl<'kvs, V> VisitSource<'kvs> for Box<V>
where
V: VisitSource<'kvs> + ?Sized,
{
fn visit_pair(&mut self, key: Key<'kvs>, value: Value<'kvs>) -> Result<(), Error> {
(**self).visit_pair(key, value)
}
}
impl<K, V, S> Source for HashMap<K, V, S>
where
K: ToKey + Borrow<str> + Eq + Hash,
V: ToValue,
S: BuildHasher,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
for (key, value) in self {
visitor.visit_pair(key.to_key(), value.to_value())?;
}
Ok(())
}
fn get(&self, key: Key) -> Option<Value<'_>> {
HashMap::get(self, key.as_str()).map(|v| v.to_value())
}
fn count(&self) -> usize {
self.len()
}
}
impl<K, V> Source for BTreeMap<K, V>
where
K: ToKey + Borrow<str> + Ord,
V: ToValue,
{
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
for (key, value) in self {
visitor.visit_pair(key.to_key(), value.to_value())?;
}
Ok(())
}
fn get(&self, key: Key) -> Option<Value<'_>> {
BTreeMap::get(self, key.as_str()).map(|v| v.to_value())
}
fn count(&self) -> usize {
self.len()
}
}
#[cfg(test)]
mod tests {
use crate::kv::value;
use super::*;
#[test]
fn count() {
assert_eq!(1, Source::count(&Box::new(("a", 1))));
assert_eq!(2, Source::count(&vec![("a", 1), ("b", 2)]));
}
#[test]
fn get() {
let source = vec![("a", 1), ("b", 2), ("a", 1)];
assert_eq!(
value::inner::Token::I64(1),
Source::get(&source, Key::from_str("a")).unwrap().to_token()
);
let source = Box::new(None::<(&str, i32)>);
assert!(Source::get(&source, Key::from_str("a")).is_none());
}
#[test]
fn hash_map() {
let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
assert_eq!(2, Source::count(&map));
assert_eq!(
value::inner::Token::I64(1),
Source::get(&map, Key::from_str("a")).unwrap().to_token()
);
}
#[test]
fn btree_map() {
let mut map = BTreeMap::new();
map.insert("a", 1);
map.insert("b", 2);
assert_eq!(2, Source::count(&map));
assert_eq!(
value::inner::Token::I64(1),
Source::get(&map, Key::from_str("a")).unwrap().to_token()
);
}
}
}
// NOTE: Deprecated; but aliases can't carry this attribute
#[cfg(feature = "kv_unstable")]
pub use VisitSource as Visitor;
#[cfg(test)]
mod tests {
use crate::kv::value;
use super::*;
#[test]
fn source_is_object_safe() {
fn _check(_: &dyn Source) {}
}
#[test]
fn visitor_is_object_safe() {
fn _check(_: &dyn VisitSource) {}
}
#[test]
fn count() {
struct OnePair {
key: &'static str,
value: i32,
}
impl Source for OnePair {
fn visit<'kvs>(&'kvs self, visitor: &mut dyn VisitSource<'kvs>) -> Result<(), Error> {
visitor.visit_pair(self.key.to_key(), self.value.to_value())
}
}
assert_eq!(1, Source::count(&("a", 1)));
assert_eq!(2, Source::count(&[("a", 1), ("b", 2)] as &[_]));
assert_eq!(0, Source::count(&None::<(&str, i32)>));
assert_eq!(1, Source::count(&OnePair { key: "a", value: 1 }));
}
#[test]
fn get() {
let source = &[("a", 1), ("b", 2), ("a", 1)] as &[_];
assert_eq!(
value::inner::Token::I64(1),
Source::get(source, Key::from_str("a")).unwrap().to_token()
);
assert_eq!(
value::inner::Token::I64(2),
Source::get(source, Key::from_str("b")).unwrap().to_token()
);
assert!(Source::get(&source, Key::from_str("c")).is_none());
let source = None::<(&str, i32)>;
assert!(Source::get(&source, Key::from_str("a")).is_none());
}
}
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