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To_ary

As explained in The Well-Grounded Rubyist, Fourth Edition

to_ary is Ruby's implicit array-conversion method for providing an Array-compatible representation when an actual array is required.

to_ary is Ruby’s implicit array-conversion method. It lets an object play the role of an Array when an operation requires an array specifically, rather than merely something that can be converted generally. section 7.4.4

Making a Person behave like an array

A Person object can expose selected attributes as an array: `def to_ary; [name, age, email]; end`. After `array = []`, calling `array.concat(person)` adds the person’s name, age, and email values to the target array.

Keep to_ary distinct from broader array construction:

  • `Array(obj)` calls `to_ary` first, then tries `to_a`; without either method, it wraps the object in a one-element array. section 9.2.1
  • Use the convention carefully: to_ary should provide a sensible array-compatible representation, not an unrelated value. section 7.4.4

How The Well-Grounded Rubyist, Fourth Edition covers it

How deep it goes
Explains definition, implicit invocation, conversion order, and invalid return behavior without descending into Ruby implementation internals.
Examples
Uses Person attributes, Array#concat, String conversion, and Array.try_convert to demonstrate successful and failing conversions.
What it assumes
Assumes familiarity with Ruby objects, methods, arrays, and classes while teaching implicit conversion through concrete examples.
What you can do after
Build it from scratch by defining to_ary to return an object’s sensible Array representation and testing it with array operations.
How it connects
Connects to to_str, to_a, Array, Array#concat, and Array.try_convert through Ruby’s implicit conversion conventions.
Cover of The Well-Grounded Rubyist, Fourth Edition
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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.