Ruby Intro

SENG2021

Functions

Firstly the syntax. Let’s first define a very basic function we can use for this post.

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def print_stuff(str1, str2, reverse = false)
  if reverse
    puts "#{str2} and #{str1} received!"
  else
    puts "#{str1} and #{str2} received!"
  end
  str = str1 + str2
end

Calling functions

Brackets around function parameters is optional in Ruby. However, sometimes it’s useful to include them regardless for clarity’s sake.

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print_stuff("First argument", "Second argument")
# First argument and Second argument received!

print_stuff "First argument", "Second argument"
# First argument and Second argument received!

Arguments can be made optional by giving them a default value.

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print_stuff("First argument", "Second argument", false)
# First argument and Second argument received!

print_stuff("First argument", "Second argument", true)
# Second argument and First argument received!

Return value

As you may have already noticed, print_stuff does use return even though it does exist in Ruby and it does exactly what you’d expect. If the return value is not specified, Ruby will return the value returned in the last executed line of the block

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def add(a, b)
  a + b
end

puts add(1, 2)
# 3

def add_return(a, b)
  return a + b
end

puts add_return(1,2)
# 3

def add_print(a, b)
  a + b
  print "add successful"
end

puts add_print(1,2)
# add successful

Because print "add successful" returns nil, add_print returns nil.

Error Handling

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def do_something
  raise "Failed to do something"
end

do_something
# RuntimeError: Failed to do something

begin
  do_something
  puts "Done something"
rescue
  puts "Rescuing from exception"
end
# Rescuing from exception

retry will return the cursor to start of the begin block it belongs to

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i = 0
begin
  puts "#{i}"
  i += 1
  if i < 2
    do_something
  end
  puts "All done!"
rescue
  retry
end
# 0
# 1
# All done!

Also relevant later on, Closures and Metaprogramming