I am using the quaternion gem and want to define a class method for the :[] operator that creates a new Quaternion from an array. I have tried
Quaternion.class_eval do
def self.[ary]
Quaternion.new(*ary)
end
end
but this gives a syntax error. How do I do this?
The method's name is [], but it still takes its argument list in the usual way
def self.[](ary)
...
end
Then you call it as Quaternion[ary]
So long story short to be able to make use of Quaternion[arg] you want to define it like below
def self.[](arg)
Quaternion.new(*ary)
end
interesting is, why does it work? Well it's syntactic sugar that ruby has
doing foo[bar] is the same as foo.[](bar)
foo[bar]=baz is the same as foo.[]=(bar, baz)
and a + b is actually a.+(b)
If you want to define it, it will look like this:
def [](key)
...
end
def []=(key, value)
...
end
def +(arg)
...
end
It's because method names in ruby can have special characters.
If you are interested in how internally it gets tokenized and parsed you can read Ruby Under Microscope which is a great introduction to the subject. There is also this free book I've found which also touches on the topic -> https://ruby-hacking-guide.github.io/ (check chapter 8 section Method Calls)