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Conditional modifier

As explained in The Well-Grounded Rubyist, Fourth Edition

A conditional modifier is postfix Ruby syntax that conditionally executes a statement without enclosing it in a compound conditional block.

A conditional modifier places if or unless after a statement, so Ruby executes that statement only when the condition permits it. For a simple condition, this avoids an enclosing end. section 6.1.1

Postfix if and unless

puts "Big number!" if x > 100 is equivalent to a multiline if/end form. The inverse style, puts "Big number!" unless x <= 100, expresses the same kind of one-statement decision. section 6.1.1

Use conditional modifiers when:

  • The condition controls one straightforward statement. section 6.1.1
  • Avoid them when branching needs else or elsif, or when the trailing statement becomes long and difficult to read. section 6.1.1
if condition
  # code here, executed if, and only if, condition is true
end

Compare the postfix examples with the ordinary if/end structure to see how the modifier removes the enclosing block. section 6.1.1

How The Well-Grounded Rubyist, Fourth Edition covers it

How deep it goes
Explains postfix syntax, equivalent block forms, branching limits, and a readability warning.
Examples
Uses puts statements guarded by postfix if and unless, alongside equivalent multiline if/end code.
What you can do after
Apply it via Ruby syntax to write concise conditional statements and recognize when a block form reads better.
How it connects
Connects conditional modifiers to if, unless, else, elsif, and statement readability.
Cover of The Well-Grounded Rubyist, Fourth Edition
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of The Well-Grounded Rubyist, Fourth Edition. The section links point to the parts of the book it draws on.