Leon's Blogging

Coding blogging for hackers.

Ruby - (&.) the Safe Navigation Operator Like Rails Try!

| Comments

ruby 2.3.0 之後有提供一個方法 &. 跟 rails 的 try! 一樣（是有 ! 驚嘆號的）

try! 跟 try 比起來比較嚴謹，會去 check receiver 是否為 nil，如果都用只用 try，反而會導致都回傳 nil 而發生錯誤時也不知道在哪

1
2
3
4
5
6
7

def try(*a, &b)
  if a.empty? && block_given?
    yield self
  else
    __send__(*a, &b)
  end
end

1
2
3
4
5
6
7

def try!(*a, &b)
  if a.empty? && block_given?
    yield self
  else
    public_send(*a, &b)
  end
end

nil

rails 5.2.3

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

class Account
  attr_reader :owner
  def initialize(owner)
    @owner = owner
  end
end

user = Account.new(nil)
user.owner.address
#NoMethodError (undefined method `address' for nil:NilClass)
user && user.owner && user.owner.address
# => nil
user.try(:owner).try(:address)
# => nil
user.try!(:owner).try!(:address)
# => nil
user&.owner&.address
# => nil

ruby 2.6.1

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

class Account
  attr_reader :owner
  def initialize(owner)
    @owner = owner
  end
end

user = Account.new(nil)
user.owner.address
# NoMethodError (undefined method `address' for nil:NilClass)
user && user.owner && user.owner.address
# => nil
user.try(:owner).try(:address)
# => undefined method `try' for #<Account:0x00007fa43d0e25e8 @owner=nil>
user.try!(:owner).try!(:address)
# => NoMethodError (undefined method `try!' for #<Account:0x00007fa43d0e25e8 @owner=nil>)
user&.owner&.address
# => nil

false

rails 5.2.3

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

class Account
  attr_reader :owner
  def initialize(owner)
    @owner = owner
  end
end

user = Account.new(false)
user.owner.address
# NoMethodError (undefined method `address' for false:FalseClass)
user && user.owner && user.owner.address
# => false
user.try(:owner).try(:address)
# => nil
user.try!(:owner).try!(:address)
# NoMethodError (undefined method `address' for false:FalseClass)
user&.owner&.address
# NoMethodError (undefined method `address' for false:FalseClass)

ruby 2.6.1

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

class Account
  attr_reader :owner
  def initialize(owner)
    @owner = owner
  end
end

user = Account.new(false)
user.owner.address
# NoMethodError (undefined method `address' for false:FalseClass)
user && user.owner && user.owner.address
# => false
user.try(:owner).try(:address)
# => NoMethodError (undefined method `try' for #<Account:0x00007fd8c78c9b08 @owner=false>)
user.try!(:owner).try!(:address)
# NoMethodError (undefined method `address' for false:FalseClass)
user&.owner&.address
# NoMethodError (undefined method `address' for false:FalseClass)

Object.new

rails 5.2.3

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

class Account
  attr_reader :owner
  def initialize(owner)
    @owner = owner
  end
end

user = Account.new(Object.new)
user.owner.address
# NoMethodError (undefined method `address' for #<Object:0x00007fcb887785e8>)
user && user.owner && user.owner.address
# NoMethodError (undefined method `address' for #<Object:0x00007fcb887785e8>)
user.try(:owner).try(:address)
# => nil
user.try!(:owner).try!(:address)
# NoMethodError (undefined method `try!' for #<Account:0x00007fd8c7893800 @owner=#<Object:0x00007fd8c7893828>>)
user&.owner&.address
# NoMethodError (undefined method `address' for #<Object:0x00007fd8c7893828>)

ruby 2.6.1

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

class Account
  attr_reader :owner
  def initialize(owner)
    @owner = owner
  end
end

user = Account.new(Object.new)
user.owner.address
# NoMethodError (undefined method `address' for #<Object:0x00007fcb887785e8>)
user && user.owner && user.owner.address
# NoMethodError (undefined method `address' for #<Object:0x00007fcb887785e8>)
user.try(:owner).try(:address)
# => NoMethodError (undefined method `try' for #<Account:0x00007fd8c7893800 @owner=#<Object:0x00007fd8c7893828>>)
user.try!(:owner).try!(:address)
# NoMethodError (undefined method `try!' for #<Account:0x00007fd8c7893800 @owner=#<Object:0x00007fd8c7893828>>)
user&.owner&.address
# NoMethodError (undefined method `address' for #<Object:0x00007fd8c7893828>)

參考文件:

Comments