Rust Variable, Constants and Shadowing

Variables¶

Before understanding variables we need to understand that Rust is a statically and strongly typed language.
We can either explicitly define the types or leave it to the compiler to infer it which known as implicit type assignment.
- let x = 4 : implicit type assignment. You cannot change the type of the variable throughout the program.
By default in rust all variables are immutable. To fix this we use the keyword mut
- let mut x = 4;
You can redefine variables in rust. This is another way of assigning a different value to a variable if you don't want to use mut.
- This is not allowed in most other programming languages.
```
fn main(){
 let x = 4;
 let x = 5;
}
```
While redefining variables we can change their type. Like from int to string.

Name Shadowing¶

fn main() {
    let x = 4;
    println!("Value of x: {}",x);

    {
        let x = x - 2;
        println!("Value of x : {}",x);
    }

    let x = x + 1;
    println!("Value of x: {}", x);
}

- Output: 4,2,5

Constants¶

Naming convention is to use all upper case letters separated by underscores.
When you define a constant you need to define its type. This is compulsory. Defining the type was optional with normal variables.
- const TIME_SECONDS: u32 = 60;

Unlike a variable constants cannot be redefined.

fn main(){
 const TIME_SECONDS: u32 = 60;
 // this wrong and will give an error
 const TIME_SECONDS: u32 = 67;
}

Last updated: 2022-05-15