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04_Archive/Inbox-Clippings/2023/03/Scope and Shadowing - Rust By Example.md

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+---
+page-title: "Scope and Shadowing - Rust By Example"
+url: https://doc.rust-lang.org/rust-by-example/variable_bindings/scope.html
+date: "2023-03-23 13:59:16"
+---
+## [Scope and Shadowing](https://doc.rust-lang.org/rust-by-example/variable_bindings/scope.html#scope-and-shadowing)
+
+Variable bindings have a scope, and are constrained to live in a *block*. A block is a collection of statements enclosed by braces `{}`.
+
+``` rust
+fn main() {
+    // This binding lives in the main function
+    let long_lived_binding = 1;
+
+    // This is a block, and has a smaller scope than the main function
+    {
+        // This binding only exists in this block
+        let short_lived_binding = 2;
+
+        println!("inner short: {}", short_lived_binding);
+    }
+    // End of the block
+
+    // Error! `short_lived_binding` doesn't exist in this scope
+    println!("outer short: {}", short_lived_binding);
+    // FIXME ^ Comment out this line
+
+    println!("outer long: {}", long_lived_binding);
+}
+```
+
+Also, [variable shadowing](https://en.wikipedia.org/wiki/Variable_shadowing) is allowed.
+
+``` rust
+fn main() {
+    let shadowed_binding = 1;
+
+    {
+        println!("before being shadowed: {}", shadowed_binding);
+
+        // This binding *shadows* the outer one
+        let shadowed_binding = "abc";
+
+        println!("shadowed in inner block: {}", shadowed_binding);
+    }
+    println!("outside inner block: {}", shadowed_binding);
+
+    // This binding *shadows* the previous binding
+    let shadowed_binding = 2;
+    println!("shadowed in outer block: {}", shadowed_binding);
+}
+
+```
+