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https://github.com/leo424y/clean-code-ruby

避免副作用

一個變數指一件事，函數作用後是另件事了

Bad:

# Global variable referenced by following function.
# If we had another function that used this name, now it'd be an array and it could break it.
$name = 'Ryan McDermott'

def split_into_first_and_last_name
  $name = $name.split(' ')
end

split_into_first_and_last_name()

puts $name # ['Ryan', 'McDermott']

Good:

def split_into_first_and_last_name(name)
  name.split(' ')
end

name = 'Ryan McDermott'
new_name = split_into_first_and_last_name(name)

puts name # 'Ryan McDermott'
puts new_name # ['Ryan', 'McDermott']

再避免副作用

再次避免搞混變數及函式

Bad:

def add_item_to_cart(cart, item)
  cart.push(item: item, time: Time.now)
end

Good:

def add_item_to_cart(cart, item)
  cart + [{ item: item, time: Time.now }]
end