From 20dd593509db111575a370a156d716a0bc851312 Mon Sep 17 00:00:00 2001
From: Jordan Gong <jordan.gong@protonmail.com>
Date: Sun, 6 Sep 2020 19:15:42 +0800
Subject: Using anonymous functions(closures)

---
 closures/src/main.rs | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 closures/src/main.rs

(limited to 'closures/src/main.rs')

diff --git a/closures/src/main.rs b/closures/src/main.rs
new file mode 100644
index 0000000..91bd189
--- /dev/null
+++ b/closures/src/main.rs
@@ -0,0 +1,59 @@
+use std::thread;
+use std::time::Duration;
+
+struct Cacher<T>
+where
+    T: Fn(u32) -> u32,
+{
+    calculation: T,
+    value: Option<u32>,
+}
+
+impl<T> Cacher<T>
+where
+    T: Fn(u32) -> u32,
+{
+    fn new(calculation: T) -> Cacher<T> {
+        Cacher {
+            calculation,
+            value: None,
+        }
+    }
+
+    fn value(&mut self, arg: u32) -> u32 {
+        match self.value {
+            Some(v) => v,
+            None => {
+                let v = (self.calculation)(arg);
+                self.value = Some(v);
+                v
+            }
+        }
+    }
+}
+
+fn generate_work(intensity: u32, random_number: u32) {
+    let mut expensive_clourse = Cacher::new(|num| {
+        println!("calculating slowly...");
+        thread::sleep(Duration::from_secs(2));
+        num
+    });
+
+    if intensity < 25 {
+        println!("Today, do {} pushups!", expensive_clourse.value(intensity));
+        println!("Next, do {} situps!", expensive_clourse.value(intensity));
+    } else {
+        if random_number == 3 {
+            println!("Take a break today! Remember to stay hydrated!");
+        } else {
+            println!("Today, run for {} minutes!", expensive_clourse.value(intensity));
+        }
+    }
+}
+
+fn main() {
+    let simulated_user_specified_value = 10;
+    let simulated_random_number = 7;
+
+    generate_work(simulated_user_specified_value, simulated_random_number);
+}
-- 
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