added closure examples

Author: BartMassey

README.md

@@ -58,3 +58,4 @@ in a controlled repository now.
 * `iterator-example.rs`: example of Rust iterator
 * `lifetimes-example.rs`: example involving Rust lifetimes
 * `strref.rs`: example involving Rust string clones and copies
+* `closures/`: closure examples

closures/README.md

@@ -0,0 +1,5 @@
+This contains various closure things
+
+* `notaclosure`: manual implementation of closure using struct
+* `closure`: standard rust closure stuff
+* `genclosure`: closures and generic types.

closures/closure/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "closure"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+
+[[bin]]
+name = "closure"
+path = "closure.rs"

closures/closure/closure.rs

@@ -0,0 +1,26 @@
+fn triple(x: u32) -> u32 {
+    x + x + x
+}
+
+fn foo() {
+    let mut y = 2;
+    let mut f: Box<dyn FnOnce(u32) -> u32> = Box::new(|x| { y += 1; x * y });
+    println!("{}", f(4));
+    f = Box::new(|x| x + x);
+    println!("{}", f(4));
+    f = Box::new(triple);
+    println!("{}", f(4));
+}
+
+fn main() {
+    foo();
+
+    /*
+    let mut y = 2;
+    let mut powerer = move |x: u64| { y += 1; u64::pow(x, y) };
+    println!("{}", powerer(3));
+    powerer = move |x: u64| { y += 1; u64::pow(x, y) };
+    println!("{}", powerer(3));
+    println!("{}", y);
+    */
+}

closures/genclosure/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "genclosure"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+
+[[bin]]
+name = "genclosure"
+path = "genclosure.rs"

closures/genclosure/genclosure.rs

@@ -0,0 +1,29 @@
+fn repeat<F: FnMut(u32)->u32>(mut f: F, x: u32) -> u32 {
+    let z = f(x);
+    f(z)
+}
+
+struct Mutation(String);
+
+impl Mutation {
+    fn new<F: FnOnce(String)->String>(mutate: F, s: String) -> Self {
+        Mutation(mutate(s))
+    }
+}
+
+fn main() {
+    let mut y = 2;
+    println!("{}", repeat(|x| {y += 1; x * y}, 3));
+
+    let pal = |s: String|->String {s.chars().rev().collect()};
+    let mutation = Mutation::new(
+        pal,
+        "hello".to_string(),
+    );
+    println!("{}", mutation.0);
+    let mutation = Mutation::new(
+        pal,
+        "goodbye".to_string(),
+    );
+    println!("{}", mutation.0);
+}

closures/notaclosure/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "notaclosure"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+
+[[bin]]
+name = "notaclosure"
+path = "notaclosure.rs"

closures/notaclosure/notaclosure.rs

@@ -0,0 +1,20 @@
+struct PowerClosure {
+    y: u32,
+}
+
+impl PowerClosure {
+    fn new(y: u32) -> Self {
+        Self { y }
+    }
+
+    fn eval(self, x: u64) -> u64 {
+        u64::pow(x, self.y)
+    }
+}
+
+fn main() {
+    let y = 2;
+    let power = PowerClosure::new(y);
+    println!("{}", power.eval(3));
+    println!("{}", power.eval(3));
+}