Rust variables: Difference between revisions
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= Copy/Cloning Values = | = Copy/Cloning Values = | ||
<blockquote> | |||
== Stack Allocated Copies (Shallow) == | |||
<blockquote> | |||
Fixed-size variables allocated to the stack can implement the <code>Copy</code> trait.<br> | |||
This allows you to shallow copy objects through assignment. | |||
<syntaxhighlight lang="rust"> | |||
let x = 5; | |||
let mut y = x; | |||
y += 1; | |||
println!("x = {}, y = {}", x, y); | |||
// x = 5, y = 6 | |||
</syntaxhighlight> | |||
</blockquote><!-- Stack Allocated Copies --> | |||
== Heap Allocated Copies (Deep) == | |||
<blockquote> | <blockquote> | ||
<syntaxhighlight lang="rust"> | <syntaxhighlight lang="rust"> | ||
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let foo_copy = foo_orig.clone(); // new allocation in heap | let foo_copy = foo_orig.clone(); // new allocation in heap | ||
</syntaxhighlight> | </syntaxhighlight> | ||
</blockquote><!-- Heap Allocated Copies (Deep) --> | |||
</blockquote><!-- Copy/Cloning Values --> | </blockquote><!-- Copy/Cloning Values --> | ||
Revision as of 15:45, 7 February 2023
Declaration
You may declare variables in rust, but it is not necessary.
let foo: u8;
Assignment
let age: u8 = 200; // typed let age = 200u8; // type-suffix let age = 200; // implied type let age: i32 = age; // type cast from 'u8' to 'i32' // conditional assignment let weather = if season == "fall" { "lovely" } else { "fine I guess" } // loop assignment let result = loop { break 123 } // break can be passed a return val
Literals
Literal types can be declared without assigning a type.
let float = 3.14; // f64 let integer = 7; // i32
Constants
Constants can be declared in any scope (including global).
constants cannot be changed once assigned.
memory addresses for the same const will not be the same (const is inlined where used).const SALT: &str = "$6$r1ohStL5/UwpNnls"; // inlined where used static RETRIES: i8 = 5; // not-inlined where used (same mem-addr)
Scope
Variable scope is bound to the block they are defined in
{ ... }
.
Blocks may be defined arbitrarily to create inner scopes.
Variables defined in outer scopes are accessible in inner scopes.fn foo() { let foo = 1; { println!("{}", foo); } }
Access Control
Everything is private in rust by default, unless explicitly declared otherwise.
Elements are declared public with thepub
modifier.fn foo() { ... } // private function pub fn foo() { ... } // public function
Mutability and Freezing
Mutability
All variables are immutable by default in rust.
You can make them mutable with themut
modifier.let mut age: i8 = 30; age += 1;Freezing
You can bind mutable variables as immutable within inner scopes.
This will prevent them from being modified within that scope.
This is known as freezing a variable.let mut age: i8 = 30; { let age = age; // immutable until block scope ends }Shadowing
You can shadow immutable variables, the result is effectively a new variable.
// valid! let height = 2; println!("{height}"); let height = 3; println!("{height}");
Shadowing/Type Conversion
let num = "32"; let num: i8 = num.parse().unwrap(); // converts 'str' to 'i8'
Copy/Cloning Values
Stack Allocated Copies (Shallow)
Fixed-size variables allocated to the stack can implement the
Copy
trait.
This allows you to shallow copy objects through assignment.let x = 5; let mut y = x; y += 1; println!("x = {}, y = {}", x, y); // x = 5, y = 6Heap Allocated Copies (Deep)
// copy pointer let foo_orig = String::from("foo"); let foo_copy = foo_orig; // deep copy let foo_orig = String::from("foo"); let foo_copy = foo_orig.clone(); // new allocation in heap
Introspection
Easiest way is to call a method on it that doesn't exist.
the stacktrace will have the type.let foo = 123; foo.cuss(); // <-- invalid method