Ruby setter-methods: Is the equal-character (=) a convention or functionality?

Question

Taken this class as a example:

class House
  def initialize(color, size)
    @color = color
    @size = size
  end

  def color
    @color
  end
  # Is the = part of the syntax or a convention?
  def color=(color)
    @color = color
  end
end

Is the equal '=' at the end of the setter-method a convention, like the '!' or the '?'? Or does is add functionality?

Answer 1

It is “only” a convention, like ending methods returning a boolean with ? or adding a ! when there is a less dangerous counterpart method.

You could define the setter method with (Java style)

def set_color(color)
  @color = color
end

or even using Unicode

def 🎨(color)
  @color = color
end

and it wouldn't make any difference at runtime.

Btw in this example, you could also use

attr_writer :color

See attr_writer, attr_reader, and attr_accessor.