只能在以下代码中的某些情况下调用链式方法。
class Klass
def foo
puts 'foo'
self
end
def bar
puts 'bar'
self
end
end
klass = Klass.new
a = 2
id = klass.foo{conditionally chain bar if a == 2}.bar
您可以在有条件地继续或停止方法链的链式方法之间插入表达式或方法吗?
这很简单,在您立即理解之后将会到来:
klass = klass.foo
klass = klass.bar if a == 2
etc...
如果链式方法不带参数,这很有效
klass.define_singleton_method :chain_if do |b, *s|
return unless b
klass = self
s.each do |x|
klass = klass.send x
end
klass
end
klass.foo.chain_if(true, :foo, :bar).chain_if(false, :bar)
这里有一些重复的线程!
Add method to an instanced object
在这里,我发现了另一个我个人喜欢的解决方
my_object.tap{|o|o.method_a if a}.tap{|o|o.method_b if b}.tap{|o|o.method_c if c}
编辑:
小心点击定义如下:
class Object
def tap
yield self
self
end
end
如果链式方法返回一个新的不可变对象,那么您需要的内容可能如下所示:
class Object
def tap_and_chain
yield self
end
end
def chain_maybe(klass, condition, *args)
args[1..-1].reduce(klass.send(args.first)) { |r,m| (condition && r.send(m)) || r }
end
要么:
def chain_maybe(klass, condition, *args)
first, *others = args
others = [] unless condition
others.reduce(klass.send(first)) { |r,m| r.send(m) }
end
对于:
class Klass
def foo
puts 'foo'
self
end
def bar
puts 'bar'
self
end
def baz
puts 'baz'
self
end
end
c = Klass.new
chain_maybe(c, true, :foo, :bar, :baz)
foo
bar
baz
#=> #<Klass:0x007fccea8da388>
chain_maybe(c, false, :foo, :bar, :baz)
foo
#=> #<Klass:0x007fccea8da388>
chain_maybe(c, true, :foo, :bar)
foo
bar
#=> #<Klass:0x007fccea8da388>
chain_maybe(c, true, :bar, :baz)
bar
baz
#=> #<Klass:0x007fccea8da388>
如果每个参数都有条件,可以推广到:
def chain_maybe(klass, conditions, args)
return nil if conditions.empty?
first, *others = args.zip(conditions).select(&:last).map(&:first)
others.reduce(klass.send(first)) { |r,m| r.send(m) }
end
args = [:foo, :bar, :baz]
chain_maybe(c, [true, true, true], args)
foo
bar
baz
#=> #<Klass:0x007fccea8da388>
chain_maybe(c, [false, true, true], args)
bar
baz
#=> #<Klass:0x007fccea8da388>
chain_maybe(c, [true, false, true], args)
foo
baz
#=> #<Klass:0x007fccea8da388>