Rust Recipes

Basics

Rust Constants

Using Constants

Rust constants use const for compile-time immutable values.

Introduction to Rust Constants

Rust constants are values that remain unchanged throughout the program's execution. They are defined using the const keyword and must have their types explicitly specified. Unlike variables, constants are evaluated at compile-time, making them efficient and reliable for constant values used in multiple places.

Defining Constants

To define a constant in Rust, use the const keyword followed by the constant name, its type, and finally the value. Constant names are conventionally written in uppercase with underscores to separate words.

Differences Between Constants and Variables

  • Immutability: Constants are always immutable, while variables can be mutable.
  • Scope: Constants can be declared in any scope, including global scope, and are accessible throughout the program.
  • Type Inference: Constants require explicit type annotations, unlike variables which can use type inference.
  • Initialization: Constants must be initialized with a constant expression, whereas variables can be initialized with computations.

Usage Examples

Constants are useful for values that do not change and are shared across various parts of a program, such as configuration settings, mathematical values, or any predefined limits.

Best Practices for Using Constants

  • Use for Fixed Values: Use constants for values that are unlikely to change and are used in multiple places.
  • Naming Conventions: Follow naming conventions by using uppercase letters and underscores.
  • Documentation: Document the purpose of constants, especially if they represent magic numbers or complex configurations.

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