Ruby lambda参数

Question

此代码按预期工作(不执行任何操作,甚至不会产生警告/错误):

l = lambda {|i|}
l.call(1)

此代码生成警告(警告:块参数的多个值(0表示1)):

l = lambda {|i|}
l.call

并且此代码失败并出现错误(ArgumentError:错误的参数数量(0表示2)):

l = lambda {|i, y|}
l.call

我认为lambda需要传递所有参数.

从第二个例子我发现它不是.为什么只给出一个参数,并且按预期工作(失败并带有错误)并且有多个参数？

PS:ruby 1.8.6(2008-08-11 patchlevel 287)[universal-darwin9.0]

更新:我用ruby 1.9.1p376检查了这些样本.它按预期工作 - 第二个例子也产生错误.看起来这是1.8版本(或<= 1.8)的功能

Answer 1

Lambdas就像这样奇怪,当你有少于两个参数时,他们的行为是不同的.查看此文章以获取更多信息.

Answer 2

这个脚本将教你在Ruby中关于闭包的所有知识.

# So, what's the final verdict on those 7 closure-like entities?          
#
#                                                     "return" returns from closure
#                                    True closure?    or declaring context...?         Arity check?
#                                    ---------------  -----------------------------    -------------------
# 1. block (called with yield)       N                declaring                        no
# 2. block (&b => f(&b) => yield)    N                declaring                        no
# 3. block (&b => b.call)            Y except return  declaring                        warn on too few
# 4. Proc.new                        Y except return  declaring                        warn on too few
# 5. proc                                    <<< alias for lambda in 1.8, Proc.new in 1.9 >>>
# 6. lambda                          Y                closure                          yes, except arity 1
# 7. method                          Y                closure                          yes

Answer 3

当lambda期望参数并且我们不提供它们,或者我们提供错误数量的参数时,抛出异常.

l = lambda { |name| puts "Today we will practice #{name} meditation." }
l.call
ArgumentError: wrong number of arguments (given 0, expected 1)

我们可以使用arity方法找出预期参数的数量:

l.arity  # Output: => 1

就像方法一样,lambda接受所有以下类型的参数/参数:

• 位置参数(必需和可选)
• 单个splat参数(*);
• 关键字参数(必填和可选);
• 双splat参数(**);
• 带有和号(&)前缀的显式块参数.

以下示例说明了采用多种类型参数的lambda的语法.

# Stabby syntax
l = -> (cushion, meditation="kinhin", *room_items, time:, posture: "kekkafuza", **periods, &p) do
  p.call
end

# Regular syntax
l = lambda do |cushion, meditation="kinhin", *room_items, time:, posture:     "kekkafuza", **periods, &p|
  p.call
end

l.call("zafu", "zazen", "zabuton", "incense", time: 40, period1: "morning", period2: "afternoon" ) { puts "Hello from inside the block, which is now a proc." }

Output:
Hello from inside the block, which is now a proc.

Lambdas以与方法相同的方式处理参数.在这篇关于方法的博客文章中,对所有上述参数/参数类型有一个全面的解释.