Struct SingleValuedMapping 

pub struct SingleValuedMapping<K, V>
where
    K: Eq + Hash,
{ /* private fields */ }

A mapping where all keys return the same value.

This is an optimization for cases like column qualification where many columns from the same table all map to the same table name. Instead of storing N copies of the value, we store it once.

Example

use polyglot_sql::helper::SingleValuedMapping;
use std::collections::HashSet;

let columns = HashSet::from(["id".to_string(), "name".to_string(), "email".to_string()]);
let mapping = SingleValuedMapping::new(columns, "users".to_string());

assert_eq!(mapping.get(&"id".to_string()), Some(&"users".to_string()));
assert_eq!(mapping.get(&"name".to_string()), Some(&"users".to_string()));
assert_eq!(mapping.get(&"unknown".to_string()), None);
assert_eq!(mapping.len(), 3);

Implementations

impl<K, V> SingleValuedMapping<K, V>

where K: Eq + Hash,

pub fn new(keys: HashSet<K>, value: V) -> Self

Create a new SingleValuedMapping from a set of keys and a single value.

pub fn from_iter<I: IntoIterator<Item = K>>(keys: I, value: V) -> Self

Create from an iterator of keys and a single value.

pub fn get(&self, key: &K) -> Option<&V>

Get the value for a key, if the key exists.

pub fn contains_key(&self, key: &K) -> bool

Check if a key exists in the mapping.

pub fn len(&self) -> usize

Get the number of keys in the mapping.

pub fn is_empty(&self) -> bool

Check if the mapping is empty.

pub fn keys(&self) -> impl Iterator<Item = &K>

Iterate over all keys.

pub fn value(&self) -> &V

Get a reference to the single value.

pub fn iter(&self) -> impl Iterator<Item = (&K, &V)>

Iterate over key-value pairs (all values are the same).

Trait Implementations

impl<K, V: Clone> Clone for SingleValuedMapping<K, V>

where K: Eq + Hash + Clone,

fn clone(&self) -> SingleValuedMapping<K, V>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<K, V: Debug> Debug for SingleValuedMapping<K, V>

where K: Eq + Hash + Debug,

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

Formats the value using the given formatter.