Final Vs Const

Final Vs Const In Dart

If you do not want to change the value of a variable, then you can use either final or const in dart.

Example

void main() {
  final finalName = "Final John Doe";
  const constName = "Const John Doe";

  finalName = "Raj"; // Not Possible
  constName = "Anu"; // Not Possible

  print("Final name is " + finalName);
  print("Const name is " + constName);
}

Error: Can't assign to the final variable 'finalName'.
Error: Can't assign to the const variable 'constName'.

Const In Dart

If you need to calculate value at compile-time, it is a good idea to choose const over final. A const variable is a compile-time constant. They must be created from data that can be calculated at compile time. 100+1 is valid const expression but const date = DateTime.now(); is not.

What Is Compile Time

When you run code in the dart, it will be compiled into the format that the machine can understand. This time is called compile time. Const value should be known at compile time.

What Is Run Time

Runtime is the time when your compiled code is started running. It generally occurs after the compile time.

const total = 50+50; // Possible
const date = DateTime.now(); // Not Possible

Advantage Of Constant

• Improve Performance

Final In Dart

If the value is calculated at runtime, you can choose final for it. For. e.g if you want to calculate date on run time, you can use final date = DateTime.now(); but not const date = DateTime.now();.

final date = DateTime.now(); // Possible
const date = DateTime.now(); // Not Possible

When To Use Const

• If you know the value at compile-time, choose const for e.g. const a = 100;.

When To Use Final

• If you don’t know the value at compile-time, choose final.
• If you want a network request that can’t be changed, choose final.
• If you want to get some values from the database, choose final.
• If you want to read a local file, choose final.