Assigning methods to variables and invoking them in Ruby

example.rb

# Assuming we're in an irb terminal.

# Keep in mind: 
# * The return value of assignment in Ruby is the thing you assigned.
# * Ruby includes syntactic sugar to invoke methods with no parentheses. So `puts` is equivalent to `puts()`

# So when we write `foo = puts`, we assign `foo` the return value of puts which is always nil.
# What we're actually saying (without the sugar) is:
# `foo = puts()`

foo = puts
# => nil

# When we compare here, we're actually just comparing nil to the return value of `puts()` which is also nil.
foo == puts
# => true

# To assign to the method we need to use `method(:puts)` which return the actual method, 
# not the result of calling the method with no arguments.

foo = method(:puts)
# => #<Method: Object(Kernel)#puts>

# Now we can call it with `call`
foo.call("bar")
# bar
# => nil

# Also we can test that it's the right method in our unit tests.
foo == method(:puts)
# => true