What is "const" in Dart?

In this post we take a look at "const" keyword with some example codes.

In Dart, const is a keyword that is used to declare variables and values that are compile-time constants. A compile-time constant is a value that can be determined at compile time and is never changed at runtime.

Here’s an example of declaring a const variable in Dart:

const int x = 10;

In this example, we declare a const integer variable named x with the value of 10. Because x is a compile-time constant, its value is determined at compile time and cannot be changed at runtime.

const can also be used to create immutable data structures like lists and maps:

const List<int> numbers = [1, 2, 3];
const Map<String, int> scores = {'Alice': 100, 'Bob': 90, 'Charlie': 80};

In this example, we declare a const list of integers named numbers and a const map from strings to integers named scores. Because these data structures are declared as const, their contents cannot be changed at runtime.

One important thing to note about const is that it can only be used with values that can be determined at compile time. For example, if you try to create a const variable using a value that is determined at runtime, you will get a compile-time error. Here’s an example of what not to do:

// This code will cause a compile-time error!
int x = 10;
const int y = x;

In this code, we try to create a const integer variable named y using the value of the non-const variable x. Because x is not a compile-time constant, we get a compile-time error.

In summary, const is a keyword in Dart that is used to declare compile-time constants, which are values that can be determined at compile time and are never changed at runtime. const can be used to create immutable data structures like lists and maps, and can help to ensure that your code is correct and efficient.

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