prefer_contains

Use contains for List and String instances.

DON'T use indexOf to see if a collection contains an element.

Calling indexOf to see if a collection contains something is difficult to read and may have poor performance.

Instead, prefer contains.

BAD:

if (lunchBox.indexOf('sandwich') == -1) return 'so hungry...';

GOOD:

if (!lunchBox.contains('sandwich')) return 'so hungry...';

To enable the prefer_contains rule, add prefer_contains under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - prefer_contains

If you're instead using the YAML map syntax to configure linter rules, add prefer_contains: true under linter > rules:

linter:
  rules:
    prefer_contains: true