问题
I saw the code from here
Post.published.collect(&:views_count)
I guess it equals to
.collect { |p| p.views_count }
But I never saw this usage before, does this have a name? Where can I find more information about it?
回答1:
This is actually a rather clever hack made it into ruby 1.9.
Basically, & in front of a variable in ruby coerces it into a proc. It does that by calling to_proc. Some clever fellow (first time I saw this was in _whys code, but I won't credit him cause I don't know if he came up with it) added a to_proc method to Symbol, that is essentially {|obj| obj.send self}.
There aren't many coercians in ruby, but it seems like all of them are mostly used to do hacks like this (like !! to coerce any type into a boolean)
回答2:
It's a use of Symbol#to_proc. The & operator turns a Proc object into a block, and because Ruby 1.8.7 and newer implement Symbol#to_proc, it can be used with a symbol like :views_count. And yes, it's equivalent to {|p| p.views_count}.
来源：https://stackoverflow.com/questions/3888044/views-count-in-post-published-collectviews-count