A method with an optional parameter

问题:

Is there a way to make a method that can accept a parameter, but can also be called without one, in which case the parameter is regarded nil like the following?

some_func(variable)

some_func

回答1:

def some_func(variable = nil)
  ...
end

回答2:

Besides the more obvious option of parameters with default values, that Sawa has already shown, using arrays or hashes might be handy in some cases. Both solutions preserve nil as a an argument.

1. Receive as array:

def some_func(*args)
  puts args.count
end

some_func("x", nil)
# 2

2. Send and receive as hash:

def some_func(**args)
  puts args.count
end

some_func(a: "x", b: nil)
# 2

回答3:

You can also use a hash as argument and have more freedom:

def print_arg(args = {})
  if args.has_key?(:age)
    puts args[:age]
  end
end

print_arg 
# => 
print_arg(age: 35, weight: 90)
# => 35