Core Syntax and Structure Comparison

📖 Learning Objectives

By comparing the basic syntax of JavaScript and Rust, you will quickly grasp the core concepts of Rust. We will start with the JavaScript syntax you are familiar with and gradually introduce Rust's syntax features.

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🎯 Variable Declaration and Scope

JavaScript Variable Declaration

In JavaScript, we use var, let, and const to declare variables:

Rust Variable Declaration

Rust uses the let keyword to declare variables, which are immutable by default:

Key Differences

1. Default Immutability: Variables in Rust are immutable by default and require the mut keyword to be modified.
2. Variable Shadowing: Rust allows redeclaring a variable with the same name in the same scope.
3. Type Inference: The Rust compiler can automatically infer the variable type.

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📊 Basic Data Type Comparison

JavaScript Data Types

JavaScript is a dynamically typed language:

Rust Data Types

Rust is a statically typed language, and types are determined at compile time:

Type System Differences

1. Static vs. Dynamic: Rust checks types at compile time, while JavaScript checks at runtime.
2. Integer Types: Rust has multiple integer types (i8, i16, i32, i64, u8, u16, u32, u64).
3. Strings: Rust distinguishes between String (owned) and &str (borrowed).

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🔄 Control Flow Comparison

JavaScript Control Flow

Rust Control Flow

Control Flow Differences

1. if Expression: Rust's if can return a value, making it useful for assignments.
2. match Statement: More powerful than JavaScript's switch, supporting pattern matching.
3. Loop Syntax: Rust uses a concise for in syntax.

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🏗️ Function Definition Comparison

JavaScript Functions

Rust Functions

Function Differences

1. Type Annotations: Rust requires explicit type annotations for function parameters and return values.
2. Return Values: In Rust, the last expression in a function is automatically returned (no return keyword needed, semicolon omitted).
3. Arrow Functions: Rust does not have an equivalent to JavaScript's arrow functions, but closures serve a similar purpose.

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📚 Summary

In this module, we compared the core syntax of JavaScript and Rust. You should now have a basic understanding of:

• How to declare variables and their immutability in Rust.
• The differences in basic data types.
• The powerful control flow structures in Rust like match and if expressions.
• The syntax for defining functions with explicit types.

Next, we will explore the module systems of both languages.