ruby中的条件链

l= []
l << :method_a if a
l << :method_b if b
l << :method_c if c

l.inject(object) { |obj, method| obj.send(method) }

Object#send 执行具有给定名称的方法。 Enumerable#inject 迭代数组,同时为块提供最后返回的值和当前数组项。

如果你想让你的方法接受参数,你也可以这样做

l= []
l << [:method_a, arg_a1, arg_a2] if a
l << [:method_b, arg_b1] if b
l << [:method_c, arg_c1, arg_c2, arg_c3] if c

l.inject(object) { |obj, method_and_args| obj.send(*method_and_args) }

你可以用 tap :

my_object.tap{|o|o.method_a if a}.tap{|o|o.method_b if b}.tap{|o|o.method_c if c}

class Foo
  attr_accessor :field
    def initialize
      @field=[]
    end
    def dup
      # Note: objects in @field aren't dup'ed!
      super.tap{|e| e.field=e.field.dup }
    end
    def a
      dup.tap{|e| e.field << :a }
    end
    def b
      dup.tap{|e| e.field << :b }
    end
    def c
      dup.tap{|e| e.field << :c }
    end
end

monkeypatch:这是您想要添加到应用程序中以启用条件链接的内容

class Object
  # passes self to block and returns result of block.
  # More cumbersome to call than #chain_if, but useful if you want to put
  # complex conditions in the block, or call a different method when your cond is false.
  def chain_block(&block)
    yield self
  end
  # passes self to block
  # bool:
  # if false, returns caller without executing block.
  # if true, return result of block.
  # Useful if your condition is simple, and you want to merely pass along the previous caller in the chain if false.
  def chain_if(bool, &block)
    bool ? yield(self) : self
  end
end

样本使用

# sample usage: chain_block
>> cond_a, cond_b, cond_c = true, false, true
>> f.chain_block{|e| cond_a ? e.a : e }.chain_block{|e| cond_b ? e.b : e }.chain_block{|e| cond_c ? e.c : e }
=> #<Foo:0x007fe71027ab60 @field=[:a, :c]>
# sample usage: chain_if
>> cond_a, cond_b, cond_c = false, true, false
>> f.chain_if(cond_a, &:a).chain_if(cond_b, &:b).chain_if(cond_c, &:c)
=> #<Foo:0x007fe7106a7e90 @field=[:b]>

# The chain_if call can also allow args
>> obj.chain_if(cond) {|e| e.argified_method(args) }

这样的模式可能更适合此应用程序:

object = my_object

if (a)
  object = object.method_a(:arg_a)
end

if (b)
  object = object.method_b
end

if (c)
  object = object.method_c('arg_c1', 'arg_c2')
end

我发现这在使用命名作用域时很有用。例如:

scope = Person

if (params[:filter_by_age])
  scope = scope.in_age_group(params[:filter_by_age])
end

if (params[:country])
  scope = scope.in_country(params[:country])
end

# Usually a will_paginate-type call is made here, too
@people = scope.all

my_object.method_a if a
my_object.method_b if b
my_object.method_c if c

我使用这种模式:

class A
  def some_method_because_of_a
     ...
     return self
  end

  def some_method_because_of_b
     ...
     return self
  end
end

a = A.new
a.some_method_because_of_a().some_method_because_of_b()

如果您使用的是Rails,那么可以使用 #try . 而不是

foo ? (foo.bar ? foo.bar.baz : nil) : nil

foo.try(:bar).try(:baz)

或者,使用参数:

foo.try(:bar, arg: 3).try(:baz)

在香草ruby中没有定义,但是 isn't a lot of code .

我不会为咖啡脚本付出什么 ?. 操作人员

这里有一种更实用的编程方法。

使用 break 为了得到 tap() 返回结果。(如另一个答案中所述,tap仅在导轨中)

'hey'.tap{ |x| x + " what's" if true }
     .tap{ |x| x + "noooooo" if false }
     .tap{ |x| x + ' up' if true }
# => "hey"

'hey'.tap{ |x| break x + " what's" if true }
     .tap{ |x| break x + "noooooo" if false }
     .tap{ |x| break x + ' up' if true }
# => "hey what's up"

我最后写了以下内容:

class Object

  # A naïve Either implementation.
  # Allows for chainable conditions.
  # (a -> Bool), Symbol, Symbol, ...Any -> Any
  def either(pred, left, right, *args)

    cond = case pred
           when Symbol
             self.send(pred)
           when Proc
             pred.call
           else
             pred
           end

    if cond
      self.send right, *args
    else
      self.send left
    end
  end

  # The up-coming identity method...
  def itself
    self
  end
end


a = []
# => []
a.either(:empty?, :itself, :push, 1)
# => [1]
a.either(:empty?, :itself, :push, 1)
# => [1]
a.either(true, :itself, :push, 2)
# => [1, 2]

#yield_self #then !

my_object.
  then{ |o| a ? o.some_method_because_of_a : o }.
  then{ |o| b ? o.some_method_because_of_b : o }.
  then{ |o| c ? o.some_method_because_of_c : o }