NSArrays are tricky bastards

gistfile1.txt

#!/usr/bin/env macruby
framework 'Cocoa'

cocoa_array = NSArray.new
ruby_array  = []

puts ruby_array.count               # => 0
puts ruby_array.count { true }      # => 0
puts ruby_array.count("whatever")   # => 0

puts cocoa_array.count              # => 0
puts cocoa_array.count { true }     # => 0 # unknown: warning: passing a block to an Objective-C method - will be ignored
puts cocoa_array.count("whatever")  # => wrong number of arguments (1 for 0) (ArgumentError)


# I originally ran into this issue in the following code, where the fact that we have an NSArray,
# and not a ruby array ends up concealed by the bajillion of ruby-ish method calls such as 
# compact and map.

paths_from_clipboard = NSPasteboard.generalPasteboard.pasteboardItems
  .map { |pbi | pbi.stringForType('public.file-url') }.compact
  .map { |url | NSURL.URLWithString(url).path }
  .map { |path| Pathname.new(path) }