use std::fs::File;
use std::io::prelude::*;
+use std::collections::HashMap;
pub fn read_file(path: &str) -> Result<String, std::io::Error> {
let mut s = String::new();
y
}
}
+
+/// Wrap and cache an expensive calculation
+///
+/// This calls a closure just once for every distinct argument. Any subsequent
+/// call to `.value()` with the same argument uses the cached value.
+pub struct Cacher<T, A, V>
+where
+ T: Fn(A) -> V,
+ A: Eq + Copy + std::hash::Hash,
+ V: Copy,
+{
+ calc: T,
+ values: HashMap<A, V>,
+}
+
+impl<T, A, V> Cacher<T, A, V>
+where
+ T: Fn(A) -> V,
+ A: Eq + Copy + std::hash::Hash,
+ V: Copy,
+{
+ pub fn new(calc: T) -> Cacher<T, A, V> {
+ Cacher { calc, values: HashMap::new() }
+ }
+
+ pub fn value(&mut self, arg: A) -> V {
+ match self.values.get(&arg) {
+ Some(v) => *v,
+ None => {
+ let v = (self.calc)(arg);
+ self.values.insert(arg, v);
+ v
+ }
+ }
+ }
+}
+
+pub struct Counter5 {
+ count: u32
+}
+
+impl Counter5 {
+ pub fn new() -> Counter5 {
+ Counter5 { count: 0 }
+ }
+}
+
+impl Iterator for Counter5 {
+ type Item = u32;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ if self.count < 5 {
+ self.count += 1;
+ Some(self.count)
+ } else {
+ None
+ }
+ }
+}