Dart: final vs const

This document aims to clarify the differences between final and const in Dart programming language.

final

• final is used to declare variables whose values cannot be changed after initialization.

• A final variable can be assigned a value only once. Once assigned, it cannot be reassigned.

• A final variable does not have to be initialized at the time of declaration. It can be initialized later, but once assigned, it cannot be changed.

• Example:

    final int myNumber;
    myNumber = 42; // This is allowed
    myNumber = 56; // Error: Cannot assign to final variable
  

const

• const is used to declare variables that are compile-time constants.

• The value of a const variable must be known at compile time. This means it must be a constant expression, computed using only literals and previously declared const variables.

• const variables are implicitly final. They cannot be reassigned after initialization.

• Example:

    const int myNumber = 42; // This is allowed
    myNumber = 56; // Error: Constant variables can't be assigned a value.
  

• const can also be used to create constant values, like:

    const pi = 3.14;
  

When to Use final and const

• Use final when the value of the variable needs to be computed at runtime.

• Use const when the value can be determined at compile time. This is often the case for things like mathematical constants.

• If you're working with objects (e.g., instances of a class), final means the variable will always refer to the same object, but the object itself can still change its internal state. const on the other hand creates an unchangeable object.

Summary

In a nutshell, final is used for variables whose values will be determined at runtime and cannot be changed after initialization. const is used for variables and values that are known at compile time and are unchangeable.

Both final and const are tools for ensuring immutability and can be used to write more reliable and maintainable Dart code.

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https://github.com/KHALEDKHLYAN/Dart_Zeor_to_Hero.com!