Metadata

ID: ruby-best-practices/hash-fetch-default

Language: Ruby

Severity: Notice

Category: Best Practices

Description

This rule emphasizes the importance of using the fetch method with a default value in Ruby, rather than a custom check. This is because the fetch method correctly handles ‘falsey’ values, such as false or nil, and will return them when they are the actual value associated with a key in a hash. This prevents unexpected results that may occur when using a custom check, as it may incorrectly evaluate a ‘falsey’ value as not present and return the default value instead.

The importance of this rule lies in the accuracy and predictability of your code. It ensures that you are correctly handling all potential values in a hash and not mistakenly returning a default value when the key is present but associated with a ‘falsey’ value. This can lead to bugs that are hard to track down and fix in your code.

To abide by this rule, always use the fetch method with a default value when checking if a key is present in a hash and you want to return a default value if it isn’t. This method will correctly handle all values, including ‘falsey’ ones, and return the accurate result. For example, instead of using hash[:key] || default_value, use hash.fetch(:key, default_value).

Non-Compliant Code Examples

test = { foo: 'foo', is_bar: false }

# on a falsey value, you get unexpected results
test[:is_bar] || true # => true

Compliant Code Examples

test = { foo: 'foo', is_bar: false }

# fetch works on falsey values, so you get expected results
test.fetch(:is_bar, true) # => false