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From: duxieweb on 15 Nov 2009 07:59 sorry just was learning ruby so have some low level questions, :) in this statement: 1.upto(10) do |c| print c," " end what's the usage of "| ... |" in ruby? can't easily understand. Thanks.
From: Ralph Shnelvar on 15 Nov 2009 09:01 Sunday, November 15, 2009, 5:59:31 AM, you wrote: d> sorry just was learning ruby so have some low level questions, :) d> in this statement: d> 1.upto(10) do |c| print c," " end d> what's the usage of "| ... |" in ruby? can't easily understand. d> Thanks. I'm just learning Ruby, too .. and I found this fairly tough to wrap my head around. This is what I think I know: Almost EVERYTHING in Ruby is an object. Thus the "1" in "1.upto(10)" is an object. Object have methods that can be applied to them. Or, equivalently, objects can have messages sent to them. "upto" is method that can be applied to the integer 1. "upto" tokes an argument "10". - - - Now here's where I get vaguer. "upto" is a method that, in turn, can call subroutines. One of the subroutines it can call is ... do |c| print c," " end The object.method known as 1.upto(10) will call the subroutine do |c| print c," " end ten times. Each time it calls do |c| print c," " end it will pass a parameter to the subroutine. In this case it will pass 1 the first time, 2 the second time ... 10 the last time. The subroutine do |c| print c," " end will see that parameter as c Thus, the subroutine do |c| print c," " end has to know a fair bit about the method "upto" in order to know what "upto" will pass to the subroutine. That is, it has to know a fair bit about the public interface of "upto" and what "upto" is supposed to do. Internal implementation of "upto" is, of course, nearly irrelevant. Like in most high level languages, the names of the parameters and the arguments do not have to be the same. Thus, do |c| print c," " end is exactly equivalent to do |parm| print parm," " end I hope this helps.
From: Marnen Laibow-Koser on 15 Nov 2009 09:13 Ralph Shnelvar wrote: > Sunday, November 15, 2009, 5:59:31 AM, you wrote: > > d> sorry just was learning ruby so have some low level questions, :) > > d> in this statement: > > d> 1.upto(10) do |c| print c," " end > > d> what's the usage of "| ... |" in ruby? can't easily understand. It declares block arguments. See the sections in the Pickaxe Book on blocks. > > d> Thanks. > > I'm just learning Ruby, too .. and I found this fairly tough to wrap > my head around. This is what I think I know: > > Almost EVERYTHING in Ruby is an object. Thus the "1" in "1.upto(10)" is > an > object. Right. > > Object have methods that can be applied to them. Or, equivalently, > objects can have messages sent to them. "upto" is method that can be > applied to the integer 1. > > "upto" tokes an argument "10". Right. > > - - - > > Now here's where I get vaguer. > > "upto" is a method that, in turn, can call subroutines. Blocks -- "subroutine" is not a Ruby term. > One of the > subroutines it can call is ... > do |c| print c," " end It can call any block at all. > > The object.method known as 1.upto(10) will call the subroutine > do |c| print c," " end > ten times. > > Each time it calls > do |c| print c," " end > it will pass a parameter to the subroutine. In this case it will pass > 1 the first time, 2 the second time ... 10 the last time. Correct. > > The subroutine > do |c| print c," " end > will see that parameter as c Also correct. > > Thus, the subroutine > do |c| print c," " end > has to know a fair bit about the method "upto" in order to know what > "upto" will pass to the subroutine. No. The block has to know that upto will yield it one object. That's all it has to know. > That is, it has to know a fair > bit about the public interface of "upto" and what "upto" is supposed > to do. Nope. The block expects one object. It doesn't really care whether it's being yielded to from 1.upto(10), or ['e', 'd', :c, {:b => 3957}].each, or anything else that will yield it one object (of any kind) as an argument. In fact, you could store the block in a variable and yield to it from each of those methods in turn. > Internal implementation of "upto" is, of course, nearly > irrelevant. Totally irrelevant, actually. > > Like in most high level languages, the names of the parameters and the > arguments do not have to be the same. Thus, > do |c| print c," " end > is exactly equivalent to > do |parm| print parm," " end You're right that those are equivalent, but it has nothing to do with your statement about parameters and arguments. > > > > I hope this helps. Best, -- Marnen Laibow-Koser http://www.marnen.org marnen(a)marnen.org -- Posted via http://www.ruby-forum.com/.
From: 7stud -- on 15 Nov 2009 09:24 duxieweb wrote: > sorry just was learning ruby so have some low level questions, :) > > in this statement: > > 1.upto(10) do |c| print c," " end > > what's the usage of "| ... |" in ruby? can't easily understand. > > Thanks. The topic you want to read about is "blocks". In ruby, upto() is an iterator, which is something that produces one value at a time. To "catch" those values, you specify what's called a "block", which is like writing a method definition right next to the call to the upto() iterator: 1.upto(10) {|num| puts num} ruby then assigns each value produced by the iterator to the block's parameter variable. The longer multi line syntax looks like this: 1.upto(10) do |num| puts num puts num * 2 end Generally, you use the short syntax when there is only one line to execute inside your "method" definition". If there is more than one line inside the "method", you use the multiline form which requires that you insert 'do' between the call to the iterator and the block. There is one slight difference between the shorter syntax and the longer syntax, but it is unimportant at this point. -- Posted via http://www.ruby-forum.com/.
From: 7stud -- on 15 Nov 2009 09:26
7stud -- wrote: > duxieweb wrote: > > ruby then assigns each value produced by the iterator to the block's > parameter variable... which is delimited with the |....| you asked about! -- Posted via http://www.ruby-forum.com/. |