original posted here: https://pedromsluz.com/posts/2022/dart-basics/
There are several ways of declaring variables. This can be done using one of:
- var
- final
- const
- dynamic
Examples:
final String name = 'Darth Vader';
var colour = 'Blue';
dynamic isReal = false;
What is the diference between them?
Var
var
allows us to defined a variable that can change its value over time. It's MUTABLE
var balance = 100.0;
balance = 300.0;
TIP: avoid has much as possible to use
var
.
In the case where you dont assign a value to the variable in the same line:
var myString;
myString = 'Darth Vader'; // <-- this variable will be set to `dynamic`
Instead of the above is better to give it the type:
String myString;
myString = 'Dart Vader'; // <-- variable will be of type String
Final
final
means read-only
(can only be set once), where it is defined. It's IMMUTABLE
final String gender = 'Male'; // <-- `final`variables need to be assigned in the same line.
gender = 'Female'; // <-- not possible will throw an error
TIP: prefer final to var whenever possible
NOTE:
final
variables need to be assigned in the same line.
Const
const
defines a compile-time constant
TIP: const's are very good for performance, since dart can optimise generated coded
TIP: Prefer to use
const
overfinal
overvar
Dynamic
dynamic
allows us to opt-out
of type safe features.
var x = 10;
x = true; // <--- not valid
dynamic y = 10; // <--- Dart.. trust me. I know what I'm doing.
y = true; // <--- VALID
NOTE: Only use
dynamic
in extreme cases when there is no alternative, or for specific use cases.
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