singleton

README.md

@@ -12,6 +12,7 @@
 | [Factory Method](/creational/factory.rs) | Defers instantiation of an object to a specialized function for creating instances | ✔ |
 | [Abstract Factory](/creational/abstract_factory.rs) | Provides an interface for creating families of releated objects | ✔ |
 | [Builder](/creational/builder.rs) | Builds a complex object using simple objects | ✔ |
+| [Singleton](/creational/singleton.rs) | Restricts instantiation of a type to one object | ✔ |
 
 
 

creational/builder.rs

@@ -15,7 +15,6 @@ impl Product {
         for v in &self.parts {
             println!("{}", v);
         }
-
         println!("{0}{1}{0}", "*".repeat(10), "*".repeat(parts_list.len()));
     }
 }
@@ -128,7 +127,7 @@ fn main() {
     direct.construct();
     let product = direct.builder.get_product();
     product.list_parts();
-    // output: 
+    // output:
     /*
     ********** parts **********
     part a1

creational/singleton.rs

@@ -0,0 +1,35 @@
+use std::sync::{Arc, Mutex};
+
+#[derive(Debug)]
+struct Config {
+    db_connection_str: String,
+}
+
+fn get_config() -> Arc<Mutex<Config>> {
+    static mut CONF: Option<Arc<Mutex<Config>>> = None;
+    unsafe {
+        CONF.get_or_insert_with(|| {
+            println!("init"); // do once
+            Arc::new(Mutex::new(Config {
+                db_connection_str: "abcdef".to_string(),
+            }))
+        })
+        .clone()
+    }
+}
+
+fn main() {
+    let f1 = get_config();
+    println!("{:?}", f1);
+    // modify 
+    {
+        let mut conf = f1.lock().unwrap();
+        conf.db_connection_str = "hello".to_string();
+    }
+
+    let f2 = get_config();
+    println!("{:?}", f2);
+    let conf2 = f2.lock().unwrap();
+
+    assert_eq!(conf2.db_connection_str, "hello".to_string())
+}