Question

I’m playing with Ruby on Rails and I’m trying to create a method with optional parameters. Apparently there are many ways to do it. I trying naming the optional parameters as hashes, and without defining them. The output is different. Take a look:

# This functions works fine!
def my_info(name, options = {})
    age = options[:age] || 27
    weight = options[:weight] || 160
    city = options[:city] || "New York"
    puts "My name is #{name}, my age is #{age}, my weight is #{weight} and I live in {city}"
end


my_info "Bill"
-> My name is Bill, my age is 27, my weight is 160 and I live in New York
-> OK!

my_info "Bill", age: 28
-> My name is Bill, my age is 28, my weight is 160 and I live in New York
-> OK!

my_info "Bill", weight: 200
-> My name is Bill, my age is 27, my weight is 200 and I live in New York
-> OK!

my_info "Bill", city: "Scottsdale"
-> My name is Bill, my age is 27, my weight is 160 and I live in Scottsdale
-> OK!

my_info "Bill", age: 99, weight: 300, city: "Sao Paulo"
-> My name is Bill, my age is 99, my weight is 300 and I live in Sao Paulo
-> OK!

****************************

# This functions doesn't work when I don't pass all the parameters
def my_info2(name, options = {age: 27, weight: 160, city: "New York"})
    age = options[:age]
    weight = options[:weight]
    city = options[:city]
    puts "My name is #{name}, my age is #{age}, my weight is #{weight} and I live in #{city}"
end

my_info2 "Bill"
-> My name is Bill, my age is 27, my weight is 160 and I live in New York
-> OK!

my_info2 "Bill", age: 28
-> My name is Bill, my age is 28, my weight is  and I live in 
-> NOT OK! Where is my weight and the city??

my_info2 "Bill", weight: 200
-> My name is Bill, my age is , my weight is 200 and I live in 
-> NOT OK! Where is my age and the city??

my_info2 "Bill", city: "Scottsdale"
-> My name is Bill, my age is , my weight is  and I live in Scottsdale
-> NOT OK! Where is my age and my weight?

my_info2 "Bill", age: 99, weight: 300, city: "Sao Paulo"
-> My name is Bill, my age is 99, my weight is 300 and I live in Sao Paulo
-> OK!

What’s wrong with the second approach for optional parameters?
The second method only works if I don’t pass any optional parameter or if I pass them all.

What am I missing?

Answer 1

The way optional arguments work in ruby is that you specify an equal sign, and if no argument is passed then what you specified is used. So, if no second argument is passed in the second example, then

{age: 27, weight: 160, city: "New York"}

is used. If you do use the hash syntax after the first argument, then that exact hash is passed.

The best you can do is

def my_info2(name, options = {})
  options = {age: 27, weight: 160, city: "New York"}.merge(options)
...