If you have been writing Flutter for a while, you have probably run into one of Dart’s unusual details: unlike many other languages, Dart gives you both const and final. So when should you use each one?

const

const is the keyword for compile-time constants. Use it when the value is known ahead of compilation and will never change. In that sense, const is what most people think of as a classic constant.

Also, every const value is implicitly final, so it cannot be reassigned.

Example:

    const pi = 3.14

Another detail worth noticing is naming. In Dart, even constants are usually written in lowerCamelCase, which can feel surprising if you come from Java or another language that prefers all-uppercase constant names. Dart’s style guide recommends lowerCamelCase because:

  • all-uppercase names look awkward in several cases, especially around enums
  • constants often evolve into non-constant values, and lowerCamelCase avoids a second rename later

final

final is for runtime constants. You can assign the value only once, but the value may be produced at runtime rather than at compile time.

One important caveat is that collection types are still reference types. A final list cannot be reassigned to a different list, but the items inside that list can still be mutated. If you want deep immutability, you may need additional helpers such as UnmodifiableListView.

This is different from const, where collection contents are also treated as constant.

final is also commonly used for instance variables in classes. The main exception is static compile-time constants, where const is still the better fit.

One more thing: a final variable must always be initialized. If you leave it uninitialized, the Dart analyzer will complain.

Tip

In Flutter, if a widget exposes a const constructor, you can also place const before the constructor call:

    // ...
    Container(
      child: const Text('static text'),
    ),
    // ...

Why does that matter? Because it tells Flutter that this widget and its subtree are guaranteed not to change when the framework walks the tree after a state update. For common immutable widgets such as EdgeInsets, Color, Icon, or Text, this can reduce unnecessary rebuild work and make UI updates cheaper.

Summary

Use const when you know the exact value at compile time. Use final when the value will be assigned only once, but that assignment happens at runtime.

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