TopolearnEvery Dart program and Flutter widget starts with these declarations, and final vs const matters for performance.
A Dart program starts at void main(). Statements end with semicolons, and print writes a line.
Declare variables with:
var name = 'Dart';— type inferred (String) and fixed; you can reassign another String.- An explicit type:
int count = 0;. final— assigned once, at run time:final now = DateTime.now();.const— a compile-time constant:const maxItems = 100;. Const values are canonicalized, so two identicalconstobjects are the same instance; Flutter uses this to skip rebuildingconstwidgets.
Core types: int, double (both subtypes of num), String, bool, plus List, Set, Map, Record and Object. Everything, including numbers and null, is an object. Conversion is explicit: int.parse('42'), 3.7.toInt(), n.toString().
Strings use single or double quotes; interpolate with $name or ${expr}. Triple quotes make multi-line strings, and r'...' is a raw string.
dynamic turns off static checking for a variable — avoid it; use Object? when you truly accept anything.
Dart is statically and soundly typed: if a variable's static type is int, it really holds an int at run time. The type checker catches most mistakes before you run.
Example
void main() {
var language = 'Dart'; // String, inferred
int year = 2011;
final launched = DateTime(year);
const maxScore = 100;
year += 14;
print('$language turns ${year - launched.year}'); // Dart turns 14
double ratio = 7 / 2; // / always gives a double
int whole = 7 ~/ 2; // integer division
print('$ratio $whole'); // 3.5 3
print(int.parse('42') + maxScore); // 142
const a = [1, 2];
const b = [1, 2];
print(identical(a, b)); // true: const values are canonical
}Remember
varinfers,finalis set once,constis a compile-time constant/returns double;~/is integer division- Interpolate with
$xand${expr}
Watch out for
- Using
dynamicto silence type errors, which moves them to run time.