= Rust Scope and Mutability =

Variables in Rust are available only in their immediate context. Most are also immutable. These defaults can be relaxed with keywords.

<<TableOfContents>>

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== Mutability ==

Many variables are actually constant in Rust. To enable reassignment of a variable, it must be declared with the `mut` keyword.

{{{
fn main() {
    let mut x = 0;
    x = 1;
}
}}}



=== Shadowing ===

It is possible to shadow a variable, so as to allow re-use of a common name.

{{{
fn main() {
    let spaces = "   ";
    let spaces = spaces.len();
}
}}}

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== Scope ==

=== Global Variables ===

Rust does not allow global variables. There are two options however for declaring a value in the global context:

 1. constants (i.e. `const THRESHOLD: i32 = 10`)
 2. static variables

A static variable is simply a variable that's given the `'static` reference lifetime-it is kept for the entire lifecycle. Additionally, a `static` variable can only be declared with constant functions (i.e. declared with `const fn`) so that they can be computed at compile time.

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== Unsafe ==



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