⭐️ In Rust variables are immutable by default, so we call them Variable bindings. To make them mutable, mut keyword is used.
⭐️ Rust is a statically typed language; It checks data type at compile time. But it doesn’t require you to actually type it when declaring variable bindings. In that case, the compiler checks the usage and sets a better data type for it. But for constants and statics you must annotate the type. Types come after a colon(:)
let a = true;
let b: bool = true;
let (x, y) = (1, 2);
let mut z = 5;
z = 6;
const N: i32 = 5;
static N: i32 = 5;
The let keyword is used in binding expressions. We can bind a name to a value or a function. Also, because the left-hand side of a let expression is a ‘pattern’, you can bind multiple names to set of values or function values.
The const keyword is used to define constants. It lives for the entire lifetime of a program but have no fixed address in memory. static is used to define ‘global variable’ type facility. There is only one instance for each value, and it’s at a fixed location in memory.
💡 Always use const, instead of static. It’s pretty rare that you actually want a memory location associated with your constant, and using a const allows for optimizations like constant propagation not only in your crate but also in downstream crates.
💡 Usually statics are placed at top of the code file, outside the functions.