问题
I'm reviewing someone's ruby code and in it they've written something similar to:
class Example
attr_reader :val
def initialize(val)
@val = val
end
end
def trigger
puts self.val
end
anArray = [Example.new(10), Example.new(21)]
anArray.each(&:trigger)
The :trigger means the symbol is taken and the & transforms it into a proc?
If that's correct, is there any way of passing variables into trigger apart from using self.?
This is related but never answered: http://www.ruby-forum.com/topic/198284#863450
回答1:
is there any way of passing variables into trigger
No.
You're invoking Symbol#to_proc which does not allow you to specify any arguments. This is a convenient bit of sugar Ruby provides specifically for invoking a method with no arguments.
If you want arguments, you'll have to use the full block syntax:
anArray.each do |i|
i.trigger(arguments...)
end
回答2:
Symbol#to_proc is a shortcut for calling methods without parameters. If you need to pass parameters, use full form.
[100, 200, 300].map(&:to_s) # => ["100", "200", "300"]
[100, 200, 300].map {|i| i.to_s(16) } # => ["64", "c8", "12c"]
回答3:
This will do exactly what you need:
def trigger(ex)
puts ex.val
end
anArray = [Example.new(10), Example.new(21)]
anArray.each(&method(:trigger))
# 10
# 21
来源：https://stackoverflow.com/questions/25195698/rails-special-symbol