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