How To Use Arguments In Ruby

,

How Many Kind Of Arguments In Ruby?

We can answer: Three

  1. Required arguments

eg:

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def hello(name)
  puts "Hello #{name}"
end

In there, name is a required argument. it mean if you call hello method and do not pass an argument, the output that you see should like:

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hello()

=> ArgumentError: wrong number of arguments (given 0, expected 1)

Let pass an argument and this error will gone.

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hello('Meo Meo')

=> "Hello Meo Meo"

It’s very simple, I think we are make sence now.

  1. Default arguments

Almost like Required arguments. It has one more thing different:

That is when we pass argument in a method, we can set default value for it, and then when you call this method and unlucky forgot pass arguments for this method, your method still working, if it’s not received arguments when it is called, it will use the default value.

eg:

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def hello(name = "Meo Meo")
  puts "Hello #{name}"
end

hello("Chinh")
=> "Hello Chinh"

# if you don't pass an argument
hello()
=> "Hello Meo Meo"
  1. Optional arguments

Do you ever want to create a method and have no idea how many arguments does this method need?

Yes, we use optional arguments for this case, take a looke at the example below:

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def hello(*family)
  family.each do |name|
    puts "Hello #{name}\n"
  end
end

hello('Chinh', 'Chuot', 'Cho')

# The output:
# Hello Chinh
# Hello Chuot
# Hello Cho

Keyword Arguments

It’s a new feature has come from ruby 2.0 to higher. It like pass arguments as a hash but more powerful.

eg:

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def hello(name: 'Chinh', age: 25)
  puts "Name: #{name} - Age: #{age}\n"
end

if you call hello method with no arguments:

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hello()

It will use default value.

And then

If you pass argumets for it:

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hello('Chinh', 25)

what will it return?

Error: yes, it will response an error, but why?

Because, with keyword arguments, you need to pass argumetns like a hash you declare when initial method. (same key).

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hello(name: 'Meo')
# Hello Meo - Age: 25

hello(age: 10)
# Hello Chinh - Age: 10

hello(name: 'Chuot', age: 11)
# Hello Chuot - Age: 11

If you want to required an argument with no default value, try this:

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def hello(name:, age:)
  puts "Name: #{name} - Age: #{age}\n"
end

It mean the method need to receive “a hash” with two key name and age. if it does not revieve, error will raise.