splat

问题 Say I have a list of arguments: > (setf format-args `(t "it's ~a" 1)) (T "it's ~a" 1) How can I then "splat" or "unroll" this into a series of arguments rather than a single list argument, for supplying to the format function? i.e I would like the following function call to take place: > (format t "it's ~a" 1) For reference, I would write the following in python or ruby: format(*format-args) I'm sure it can be done, but perhaps I'm thinking about it wrong. It also doesn't help that the name

问题 In Python and Ruby (and others as well, I'm sure). you can prefix an enumerable with * ("splat") to use it as an argument list. For instance, in Python: >>> def foo(a,b): return a + b >>> foo(1,2) 3 >>> tup = (1,2) >>> foo(*tup) 3 Is there something similar in Haskell? I assume it wouldn't work on lists due to their arbitrary length, but I feel that with tuples it ought to work. Here's an example of what I'd like: ghci> let f a b = a + b ghci> :t f f :: Num a => a -> a -> a ghci> f 1 2 3 ghci

问题 If I have a procedure or a command in TCL, with variable number of arguments, one can use, if a list's elements are as an input, the "splatter" operator, for example: set a [list "ko" ] set m [ list "ok" "bang" ] lappend a {*}$m But, what if I want to "twice splatter"? I.e., flatten 2 levels? Using it twice, in sequence, does not work: set a [list "ko" ] set m [ list [ list "ok" ] [ list "bang" ] ] lappend a {*}{*}$m Will error out on extra character. 回答1: You've noticed that {*}

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed last year . I have a method that should take 1+ parameters of any class, similar to Array#push: def my_push(*objects) raise ArgumentError, 'Needs 1+ arguments' if objects.empty? objects.each do |obj| puts "An object was pushed: #{obj.inspect}" @my_array.push obj end end What is the best

问题 I am using Ruby on Rails 3 and I would like to know what means the presence of a * operator near a function argument and to understand its usages in others scenarios. Example scenario (this method was from the Ruby on Rails 3 framework): def find(*args) return to_a.find { |*block_args| yield(*block_args) } if block_given? options = args.extract_options! if options.present? apply_finder_options(options).find(*args) else case args.first when :first, :last, :all send(args.first) else find_with

问题 match, text, number = *"foobar 123".match(/([A-z]*) ([0-9]*)/) I know this is doing some kind of regular expression match but what role does the splat play here and is there a way to do this without the splat so it's less confusing? 回答1: is there a way to do this without the splat so it's less confusing? Since a,b = [c,d] is the same as a,b = *[c,d] and splat calls to_a on its operand when it's not an array you could simply call to_a explicitly and not need the splat: match, text, number =

问题 I'm assigning an array constant like this: NUMS = *(2..9) Rubocop says C: Freeze mutable objects assigned to constants. NUMS = *(2..9) ^^^^^ So I try NUMS = *(2..9).freeze Rubocop says C: Freeze mutable objects assigned to constants. NUMS = *(2..9).freeze ^^^^^^^^^^^^ Tried NUMS = (*(2..9)).freeze Rubocop says E: unexpected token tRPAREN (Using Ruby 2.0 parser; configure using TargetRubyVersion parameter, under AllCops) NUMS = (*(2..9)).freeze ^ Tried NUMS = [1, 2, 3, 4, 5, 6, 7, 8, 9].freeze

问题 A splat on a hash converts it into an array. [*{foo: :bar}] # => [[:foo, :bar]] Is there some hidden mechanism (such as implicit class cast) going on here, or is it a built-in primitive feature? Besides an array, are nil and hash the only things that disappear/change with the splat operator under Ruby 1.9? 回答1: A splat will attempt an explicit conversion of an object to an Array. To do this, it will send to_a and expect an Array as a result. class Foo def to_a [1,2,3] end end a, b, c = *Foo

问题 def initialize(apps, catch=404) @apps = []; @has_app = {} apps.each { |app| add app } @catch = {} [*catch].each { |status| @catch[status] = true } end In this method from Rack::Cascade, what purpose does the splat(*) serve in the [*catch] code? I thought a splat was used in method arguments to indicate when you are going to have an unspecified number of parameters. Does the splat have a different meaning here? 回答1: It creates a single flat array for catch I'm not sure anyone completely

问题 Why do Ruby (2.0) procs/blocks with splat arguments behave differently than methods and lambdas? def foo (ids, *args) p ids end foo([1,2,3]) # => [1, 2, 3] bar = lambda do |ids, *args| p ids end bar.call([1,2,3]) # => [1, 2, 3] baz = proc do |ids, *args| p ids end baz.call([1,2,3]) # => 1 def qux (ids, *args) yield ids, *args end qux([1,2,3]) { |ids, *args| p ids } # => 1 Here's a confirmation of this behavior, but without explanation: http://makandracards.com/makandra/20641-careful-when