No magic number
Rule id
no-magic-number
Severity
Warning
Description
Warns against using number literals outside of named constants or variables. Exceptions are made for common constants (by default: -1, 0 and 1) and for literals inside DateTime
constructor as there is no way to create const DateTime
and extracting each int
argument to separate named constant is far too inconvenient.
Example
Bad:
double circleArea(double radius) => 3.14 * pow(radius, 2); // warns against 3.14
Good:
const pi = 3.14;
double circleArea(double radius) => pi * pow(radius, 2); // using named constant so no warning
Bad:
...
final finalPrice = cart.productCount > 4 // warns against 4
? cart.totalPrice - (cart.totalPrice * 0.25); // warns against 0.25
: cart.totalPrice
...
Good:
...
const productCountThresholdForDiscount = 4;
const discount = 0.25;
final finalPrice = cart.productCount > productCountThresholdForDiscount
? cart.totalPrice - (cart.totalPrice * discount);
: cart.totalPrice
...
Exception:
final someDay = DateTime(2006, 12, 1); // DateTime has no const constructor
Config example
dart_code_metrics:
...
rules:
...
- no-magic-number:
allowed: [3.14, 100, 12]