7- dart const and final(Arabic) скачать в хорошем качестве

7- dart const and final(Arabic)

Final and const If you never intend to change a variable, use final or const, either instead of var or in addition to a type. A final variable can be set only once; a const variable is a compile-time constant. (Const variables are implicitly final.) A final top-level or class variable is initialized the first time it’s used. Note: Instance variables can be final but not const. Final instance variables must be initialized before the constructor body starts — at the variable declaration, by a constructor parameter, or in the constructor’s initializer list. Here’s an example of creating and setting a final variable: final name = 'Bob'; // Without a type annotation final String nickname = 'Bobby'; You can’t change the value of a final variable: name = 'Alice'; // Error: a final variable can only be set once. Use const for variables that you want to be compile-time constants. If the const variable is at the class level, mark it static const. Where you declare the variable, set the value to a compile-time constant such as a number or string literal, a const variable, or the result of an arithmetic operation on constant numbers: