# Why (1..4).inject(&:+) works? **URL:** \ **Category:** Ruby\ **Created:** [October 29, 2009, 7:14pm UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146 "2009-10-29T19:14:57Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 29, 2009, 7:14pm UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/1 "2009-10-29T19:14:57Z")
Hi rubyists, I was just wondering why, (1…4).inject(&:+) #=\> 10 works ? (in Ruby 1.9.2) I understand easily these: (1…4).inject { |s, e| s + e } #=\> 10 (1…4).inject(:+) #=\> 10 I suppose it’s calling :+.to\_proc #=\> #Proc:0x2f52d8 irb\> def a(&b); b; end irb\> a(&:+) =\> #Proc:0x2f52d8 irb\> :+.to\_proc =\> #Proc:0x2f52d8 irb\> p = a(&:+) =\> #Proc:0x2f52d8 irb\> p.arity =\> -1 irb\> p.call(1,2) =\> 3 irb\> p.call(1) ArgumentError: wrong number of arguments(0 for 1) … irb\> p.call(1,2,3) ArgumentError: wrong number of arguments(2 for 1) … irb\> p.call ArgumentError: no receiver given Well, that’s strange: arity = -1, so normally only optional arguments. And it expects 1 argument but want 2 ? “no receiver given” : That means it knows it has a argument to act on like a.+(b). How come ? Would &:+ knows it need some object to act with “+”(o) ? Have a nice day ---
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 29, 2009, 7:23pm UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/2 "2009-10-29T19:23:44Z")
Hi, Can anyone suggest a faster alternative to String.split()? I need to call it very intensively and its quite a hotspot. I’m using ruby 1.8.7. Cheers, James ---
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 29, 2009, 7:30pm UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/3 "2009-10-29T19:30:45Z")
On Fri, Oct 30, 2009 at 03:23:01AM +0900, James F. wrote: > Hi, > > Can anyone suggest a faster alternative to String.split()? I need to call it very intensively and its quite a hotspot. I’m using ruby 1.8.7. > > Cheers, > James use ruby inline ---
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 29, 2009, 7:39pm UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/4 "2009-10-29T19:39:32Z")
> > Can anyone suggest a faster alternative to String.split()? I need to > > call it very intensively and its quite a hotspot. I’m using ruby 1.8.7. > > > > Cheers, > > James > > use ruby inline Thanks for the link - was not aware of that. Will definitely look into that. ---
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 29, 2009, 8:04pm UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/5 "2009-10-29T20:04:43Z")
On Oct 29, 2009, at 11:23 , James F. wrote: > Can anyone suggest a faster alternative to String.split()? I need to > call it very intensively and its quite a hotspot. I’m using ruby > 1.8.7. I can suggest you not thread hijack anymore. It is rude and messes up people who use real mail clients. Start a new mail. ---
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 29, 2009, 8:23pm UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/6 "2009-10-29T20:23:17Z")
Benoit D. wrote: > Hi rubyists, > > I was just wondering why, > > (1..4).inject(&:+) #=\> 10 > > works ? (in Ruby 1.9.2) Works in 1.8.7 too, FWIW. ---
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 29, 2009, 8:53pm UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/7 "2009-10-29T20:53:51Z")
Benoit D. wrote: > “no receiver given” : That means it knows it has a argument to act on > like > a.+(b). How come ? > Would &:+ knows it need some object to act with “+”(o) ? a + b is syntactic sugar for a.+(b), or a.send(:+,b) - you can see that you have one receiver, and one argument. If you google “symbol to\_proc” you’ll find some 1.8 implementations. The first hit I get is PragDave’s blog where he shows this code: class Symbol def to\_proc proc { |obj, \*args| obj.send(self, \*args) } end end > Well, that’s strange: arity = -1, so normally only optional arguments. And > it expects 1 argument but want 2 ? You can see why that is from the implementation above. The method call must have a receiver (obj), but we know how many other arguments to take, so it accepts zero or more. It passes them all as arguments to the method, whose name is the symbol itself. ---
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 30, 2009, 1:48am UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/8 "2009-10-30T01:48:55Z")
On Thu, Oct 29, 2009 at 2:14 PM, Benoit D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > (1..4).inject { |s, e| s + e } #=\> 10 > irb\> p = a(&:+) > … > irb\> p.call > ArgumentError: no receiver given > > Well, that’s strange: arity = -1, so normally only optional arguments. And > it expects 1 argument but want 2 ? > “no receiver given” : That means it knows it has a argument to act on like > a.+(b). How come ? > Would &:+ knows it need some object to act with “+”(o) ? irb(main):001:0\> 1.send(:+) ArgumentError: wrong number of arguments(0 for 1) from (irb):1:in `+' from (irb):1 from /Users/rick/.rvm/ruby-1.9.1-p243/bin/irb:12:in `’ irb(main):002:0\> 1.send(:+, 2) =\> 3 irb(main):003:0\> 1.send(:+, 2, 3) ArgumentError: wrong number of arguments(2 for 1) from (irb):3:in `+' from (irb):3 from /Users/rick/.rvm/ruby-1.9.1-p243/bin/irb:12:in `’ – Rick DeNatale Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) Twitter: [http://twitter.com/RickDeNatale](http://twitter.com/RickDeNatale) WWR: [NameBright - Coming Soon](http://www.workingwithrails.com/person/9021-rick-denatale) LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale) ---
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 30, 2009, 9:24am UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/9 "2009-10-30T09:24:53Z")
> > call it very intensively and its quite a hotspot. I’m using ruby > > 1.8.7. > > I can suggest you not thread hijack anymore. It is rude and messes up > people who use real mail clients. Start a new mail. Was not being rude - was not aware of it. My mail client allows me to read and write text to people so its about as real as I need it to be. ---
**Author:** ![benoitdinocourt](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/87869e/32.png) [@benoitdinocourt](https://www.ruby-forum.com/u/benoitdinocourt)\ **Post date:** [October 30, 2009, 12:29pm UTC](https://www.ruby-forum.com/t/why-1-4-inject-works/178146/10 "2009-10-30T12:29:49Z")
In fact, I knew about about the 1.8 implementations. I just forgot about it. Thank to have cleared my ideas. The current implementation looks like (of course it must be in C): class Symbol def to\_proc @to\_proc ||= Proc.new { |\*args| args.shift.send(self, \*args) } end end 2009/10/30 Rick DeNatale [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)