falcon

Rules / Style / prefer-is-empty

prefer-is-empty

lint/style/prefer-is-empty
Same as prefer_is_empty · Dart lints

Flags .length comparisons equivalent to a .isEmpty check.

Collections and strings expose an isEmpty getter that states intent directly and, for lazy iterables, can be cheaper than computing the full length. Comparing length against a constant forces the reader to decode the boundary, so list.isEmpty should replace forms such as length == 0, length < 1, and length <= 0, together with their operand-swapped mirrors (0 == length, 1 > length, 0 >= length). The rule matches any .length property access against the relevant integer literal; it does not attempt to confirm the receiver actually offers isEmpty.

Invalid

example.dartdart
void bad() {
  if (list.length == 0) return;
  if (0 == items.length) return;
  if (str.length < 1) return;
  if (map.length <= 0) return;
  if (1 > set.length) return;
  if (0 >= names.length) return;
}
Use 'isEmpty' instead of comparing 'length' to 0.
1void bad() {
2 if (list.length == 0) return;
Use 'isEmpty' instead of comparing 'length' to 0.
2 if (list.length == 0) return;
3 if (0 == items.length) return;
Use 'isEmpty' instead of comparing 'length' to 0.
3 if (0 == items.length) return;
4 if (str.length < 1) return;
Use 'isEmpty' instead of comparing 'length' to 0.
4 if (str.length < 1) return;
5 if (map.length <= 0) return;
Use 'isEmpty' instead of comparing 'length' to 0.
5 if (map.length <= 0) return;
6 if (1 > set.length) return;
Use 'isEmpty' instead of comparing 'length' to 0.
6 if (1 > set.length) return;
7 if (0 >= names.length) return;

Valid

example.dartdart
void good() {
  if (list.isEmpty) return;
  if (items.length == 2) return;
  if (str.length > 0) return;
  if (map.length != 0) return;
  if (set.length >= 1) return;
  if (count == 0) return;
}

How to configure

Set the severity of prefer-is-empty in your falcon.json:

falcon.jsonjson
{
  "linter": {
    "rules": {
      "style": {
        "prefer-is-empty": "error"
      }
    }
  }
}

Related