Unless expression
An unless expression conditionally evaluates one branch when its condition is false and another branch otherwise.
The Well-Grounded Rubyist, Fourth Edition
The unless keyword introduces a conditional construct whose body executes when its condition is false.
- How it is used
- Expresses negative conditional logic in ordinary or modifier-position control flow.
- How deep it goes
- Explains false-condition execution, equivalent negation, else behavior, and modifier placement, but not implementation internals.
- Examples
- Uses number-size classification and a minimal x == 1 condition to contrast unless with if.
- What you can do after
- Apply unless to write concise negative tests and choose if/else when an else branch improves clarity.
Read how The Well-Grounded Rubyist, Fourth Edition explains unless expression →
Elixir in Action, Third Edition
An unless expression conditionally evaluates one branch when its condition is false and another branch otherwise.
- How it is used
- Expresses negative conditional logic when an action should occur unless an error or other disqualifying condition holds.
- How deep it goes
- Defines branch behavior and shows its macro-level transformation into if, without detailed macro implementation.
- Examples
- Uses notification sending to contrast an unless guard against its equivalent positive if condition.
- What you can do after
- Apply it via Elixir syntax to express negative conditions with block or one-line branches.
Read how Elixir in Action, Third Edition explains unless expression →
Related concepts
- macrokind of · A macro is a named construct that expands or transforms source code, commands, or templates before or during execution.
- conditional logicequivalent to · Conditional logic is a programming technique that selects execution paths, actions, or result values according to evaluated conditions.
- expressionkind of · An expression is a syntactic construct in a programming language that evaluates to a value or designates an object, and may also cause side effects.
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