dart: Variables Declaration

1. dart는 포멧터(formatter)가 세미콜론 ; 을 자동으로 입력해주지 않는다.

2. Variables

in case of usage of var

recommended way to use : var 

case1
var name = "type of string"; 
    name = 1 // error 
    should be string once it initialized 

case2 
var name ;  
  
    name =  'you'; //OK 
  
    name = 1;  //OK 
    
    
    
in a same way to declare variables like above 
explicitly declared with class  
String name = "type of string"; 

in case of usage of dynamic

dynamic name = "any type";
name = 1 ;  // OK 
name = true ; // OK 


be changable 

in case of usage of final

final String name = 'string' 

name = 'string 1'  // error 

cannot assign again.

in case of usage of late

late final String name; 

// do something, go to api then 

name = 'name lazy from data'; // means one assignment 

in case of usage of const

// 자바스크립트 & 타입스크립트의 const는 final과 더 흡사함.

cosnt : should be known at the compile time 
// 컴파일 단계에서 이미 알고 있는 값 : const AppId , appBundleId etc.
const API_KEY = '112121'; 

const API_KEY = fetchApi(''); //error
==> (final or var) API_KEY = fetchApi(''); // OK 

3. null safety : ? mark

 String name = 'String' 
 or 
 String? name = 'String' or null
 name?.isNotEmpty;