Differences between Proc and Lambda
Ruby has differences between Procs created via Proc.new
and lambda
(or the ->()
operator in 1.9). It appears that non-lambda Procs will splat an array passed in across the block arguments; Procs created via lambda do not.
p = Proc.new { |a,b| a + b}
p[[1,2]] # => 3
l = lambda { |a,b| a开发者_如何学Python + b }
l[[1,2]] # => ArgumentError: wrong number of arguments (1 for 2)
Does anyone have any insight into the motivations behind this behavior?
There are two main differences between lambdas and non-lambda Proc
s:
- Just like methods, lambdas return from themselves, whereas non-lambda
Proc
s return from the enclosing method, just like blocks. - Just like methods, lambdas have strict argument checking, whereas non-lambda
Proc
s have loose argument checking, just like blocks.
Or, in short: lambdas behave like methods, non-lambda Proc
s behave like blocks.
What you are seeing there is an instance of #2. Try it with a block and a method in addition to a non-lambda Proc
and a lambda, and you'll see. (Without this behavior, Hash#each
would be a real PITA to use, since it does yield an array with two-elements, but you pretty much always want to treat it as two arguments.)
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