avoid_double_and_int_checks

Explicit check for double or int.

The analyzer produces this diagnostic when an if statement tests the type of a variable with is double and the following else if tests the same variable with is int.

When compiled to JavaScript, both int and double values are represented as JavaScript Number values. Because every int value also satisfies the is double check, the is int branch is unreachable.

To learn more about how Dart represents numbers on different platforms, including when compiled to JavaScript, check out Numbers in Dart.

The following code produces this diagnostic because x is type tested with is double and then is int, which makes the is int branch unreachable when compiled to JavaScript:

void f(Object x) {
  if (x is double) {
    print('double');
  } else if (x is int) {
    print('int');
  }
}

If the distinction between int and double isn't meaningful, then check if the type is num instead:

void f(Object x) {
  if (x is num) {
    print('num');
  }
}

If both branches are needed and it's ok for integer double values (such as 3.0) to take the is int branch, then check is int first. This ensures that integer values take the is int branch on all platforms:

void f(Object x) {
  if (x is int) {
    print('int');
  } else if (x is double) {
    print('double');
  }
}