Section 1.1: The Importance of Type Systems

Type systems serve as crucial elements in programming languages. To illustrate this, let's first pose the question: "What constitutes Python's type system?"

To answer this, we must comprehend what a type system entails. In simple terms, it consists of rules that allocate specific properties (like integers or floating points) to elements (such as variables or constants) within a program.

Computers recognize only binary digits (0s and 1s), which can be quite challenging for programmers. Consequently, higher-level languages were developed to simplify and regulate these binary sequences. Essentially, a type system provides programmers with a structured way to manage binary data, enabling us to write code at a higher level.

Common classifications of type systems include:

• Statically typed: Data types are verified at compile time.
• Dynamically typed: Data types are verified at runtime.
• Strongly typed: Implicit type conversion is prohibited.
• Weakly typed: Implicit type conversion is permitted.

From these categories, we can identify four distinct types of programming languages:

1. Statically and strongly typed: Examples include Rust and Go.
2. Statically and weakly typed: Surprisingly, C falls into this category due to its allowance for implicit type conversion.
3. Dynamically and strongly typed: Python fits here, where type checking occurs during runtime, but incompatible type conversions are restricted.
4. Dynamically and weakly typed: JavaScript exemplifies this category.

Video Description: In this Rust Basics lesson, we explore variables and their mutability in-depth.

Section 1.2: Variables in Rust

At first glance, Rust's variable syntax resembles that of JavaScript (specifically ES6+). To declare a variable in Rust, we utilize the let keyword:

fn main() {

let x = 100;

println!("x is {}", x);

}

In this example, we create a variable x and assign it the value of 100. The println! macro is used for output, similar to printf in C and print in Python.

However, here lies the distinction: if we attempt to reassign x to 200, we might think to do it this way:

fn main() {

let x = 100;

println!("x is {}", x);

x = 200; // This will cause a compilation error

println!("x is {}", x);

}

It turns out that reassignment of a variable is not permitted in Rust, which can be surprising initially.

By default, all variables in Rust are immutable. To create a mutable variable, we need to add the mut keyword:

fn main() {

let mut x = 100;

println!("x is {}", x);

x = 200; // Reassignment is now allowed

println!("x is {}", x);

}

Nonetheless, this method of modifying variables isn't the most idiomatic in Rust; instead, shadowing is preferred. By declaring a variable with the same name as an existing one, the original variable gets shadowed, making the new variable visible in its scope:

fn main() {

let x = 100;

println!("x is {}", x);

let x = 200; // Shadowing occurs here

println!("x is {}", x);

}

Constants can also be defined in Rust using the const keyword:

const PI: f64 = 3.1415926;

fn circle_area(r: f64) -> f64 {

return r * r * PI;

}

fn main() {

let cir_area: f64 = circle_area(5.0);

println!("The circle area is {}", cir_area);

}

The primary distinction between constants and variables lies in when they are evaluated: constants are computed at compile time, while variables are evaluated at runtime.

For instance, a constant can be defined as follows:

const MAGIC_NUM: i32 = 40 + 3 - 1; // Calculated at compile time

However, if we try to define a constant using a function, we will encounter an error:

fn get_magic_num() -> i32 {

return 42;

}

const MAGIC_NUM = get_magic_num(); // This will result in an error