# Ruby course confusion **URL:** \ **Category:** Ruby\ **Created:** [February 12, 2006, 6:23am UTC](https://www.ruby-forum.com/t/ruby-course-confusion/66035 "2006-02-12T06:23:32Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![combas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/aca169/32.png) [@combas](https://www.ruby-forum.com/u/combas)\ **Post date:** [February 12, 2006, 6:23am UTC](https://www.ruby-forum.com/t/ruby-course-confusion/66035/1 "2006-02-12T06:23:32Z")
Working my way through the “ruby course” > **[RubyCourse\_1.0-1.pdf](https://ruby-doc.org/docs/Immersive%20Ruby%20programming%20course/RubyCourse_1.0-1.pdf)** > > 2.19 MB I was wondering if anyone else finds this tutorial a little confusing. Its really good in parts, but other parts are really unclear but maybe its just me. For example: ```auto find_it Write a function find_it that takes an array of strings and a block. The block should take two parameters and return a boolean value. The function should allow to implement longest_string, shortest_string, and other functions by changing the block. ``` Sorry, this just seems really muddled. Is find\_it a class, method, or what? What is the point of the boolean that the block needs to return? I asume that find\_it is a class, and longest\_string and shortest\_string are object methods, and the array and the block are passed when the class is initialized, but I feel like I’m missing something. ---
**Author:** ![combas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/aca169/32.png) [@combas](https://www.ruby-forum.com/u/combas)\ **Post date:** [February 12, 2006, 7:01am UTC](https://www.ruby-forum.com/t/ruby-course-confusion/66035/2 "2006-02-12T07:01:52Z")
On Feb 12, 2006, at 5:23, Alex C. wrote: > Sorry, this just seems really muddled. > Is find\_it a class, method, or what? > What is the point of the boolean that the block needs to return? > > I asume that find\_it is a class, and longest\_string and > shortest\_string > are object methods, and the array and the block are passed when > the class is initialized, but I feel like I’m missing something. A function in this case would be a method. The two terms are often used interchangeably, despite theoretical quibbles that they’re not quite the same thing; a lambda expression is also a function, for instance. The point of the block is that you’re attempting to write a method that can be used as a general implementation of several other methods, depending on the contents of the block. The boolean return value of the block is actually a very small hint, following from the fact that finding the shortest/longest element of an array is very closely related to sorting the array. Anyway, here’s the initial problem restated: > def longest\_string (arr) > find\_it(arr) { … } > end > > def shortest\_string (arr) > find\_it(arr) { … } > end As for the document being muddled, I read a fair bit of it, and it strikes me that the amount of apparent muddle would depend on your previous exposure to programming in general. It’s a bit of a catch with teaching/learning programming; it uses very jargony language without the same formalism you get in maths. A method in one language is a function in another is a procedure in a third and doesn’t even exist as a concept in a fourth language. This vocabulary issue really does put a hitch in learning programming, since to know what a term really means, you need to know the theory behind it, for which you need to know what the terms mean… and I think you see the problem. The best way to deal with this obstacle it is to jump right in, and ask questions when you’re stumped. Which you seem to be doing, so good on you. Hope that helps. matthew smillie. * * * Matthew S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Institute for Communicating and Collaborative Systems University of Edinburgh ---
**Author:** ![combas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/aca169/32.png) [@combas](https://www.ruby-forum.com/u/combas)\ **Post date:** [February 12, 2006, 9:16pm UTC](https://www.ruby-forum.com/t/ruby-course-confusion/66035/3 "2006-02-12T21:16:54Z")
On 2/11/06, Matthew S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: Thanks Matthew, I appreciate you taking the time to reword this for me, but there is one part that is still bothering me. > > The block should take two parameters and return a boolean value. Its the thing with the boolean that I dont get. This seems to be asuming some prior knowledge of a particular ruby method. I’ve searched Array and String and dont see anything that fits. What is this boolean supposed to show? Booleans can me on/off true/false, found/not\_found, or many other things. If the guide just stated what the boolean is for, or even better what method they want used that returns a boolean I’m sure this would be a rather simple problem. Finding the longest or shortest string in an array is so trivial. This really seems more like an exercise on howto structure blocks and pass variables to methods. result = arr.sort\_by {|w| w.length}; shortest,longest = result[0],result[-1] ---
**Author:** ![combas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/aca169/32.png) [@combas](https://www.ruby-forum.com/u/combas)\ **Post date:** [February 12, 2006, 9:32pm UTC](https://www.ruby-forum.com/t/ruby-course-confusion/66035/4 "2006-02-12T21:32:12Z")
DÅ?a Nedeľa 12 Február 2006 21:16 Alex C. napísal: > I’ve searched Array and String and dont see anything that fits. > and pass variables to methods. > D’oh. What I think are strong hints follows. Don’t read this mail if you don’t want any. I think the block should be a predicate that defines if something was “found” - that’s what the boolean it returns should tell. Or rather evaluate if an element is more “it” than the previous one found. As for the two parameters, I think one should be an element from the array that’s being iterated on, and another the last element for which the block returned true. Let Enumerable#inject be an inspiration, I believe #find\_it is supposed to have similar swissknifeitude. (Groan) Alright, but I’m getting dangerously close to giving away complete spoilers, so I’ll leave you some challenge to the problem. David V. ---
**Author:** ![combas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/aca169/32.png) [@combas](https://www.ruby-forum.com/u/combas)\ **Post date:** [February 13, 2006, 1:52am UTC](https://www.ruby-forum.com/t/ruby-course-confusion/66035/5 "2006-02-13T01:52:52Z")
On Feb 12, 2006, at 20:16, Alex C. wrote: > On 2/11/06, Matthew S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > The block should take two parameters and return a boolean value. > > Its the thing with the boolean that I dont get. This seems to be > asuming > some prior knowledge of a particular ruby method. > I’ve searched Array and String and dont see anything that fits. Well, it’s meant to illustrate a very handy property of blocks, but it doesn’t assume anything about knowledge of a particular Ruby method. It does seem to assume some previous knowledge of how searching and sorting works, though. > What is this boolean supposed to show? Booleans can me on/off > true/false, found/not\_found, or many other things. Booleans don’t mean anything by themselves, the semantics is imposed by how they’re used. Let’s say I give you two methods that operate on two strings: is\_shorter? and is\_longer? The boolean value ‘true’ has two precisely opposite meanings. So in this case, the semantics of the boolean value is dependent only on what happens in the block. The method calling the block (i.e. find\_it) will treat ‘true’ in the same way no matter what its particular semantics are. For example, “true” could mean “the first argument is shorter than the second” or vice-versa. It could mean that the first argument has more vowels than the second. It could mean that the first argument starts with a letter closer to ‘a’ than the second argument. Passing any of these blocks to find\_it will change exactly what’s being found. (This is a big hint.) > If the guide just stated what the boolean is for, or even better what > method they want used that returns a boolean I’m sure this would > be a rather simple problem. Well, from the above examples, I hope it’s clear that they don’t have any particular method in mind that returns a boolean. Just that there’s a block which takes two things, and returns a boolean value. find\_it will deal with a ‘true’ result from one block in exactly the same way as it deals with a ‘true’ result from any other block, and what that means only depends on the block. David gave you a few big hints, so I’ll go one baby step further to start you off: reduce the problem to a simpler one. Assume that you’re trying to implement longest\_string by doing only pair-wise comparisons. The comparison is done by a separate method which takes two strings and returns true/false. You’ll need to decide the following questions, among others: - What does a ‘true’ result from the comparison method mean? - HOw should you order the comparisons to get the desired overall result? I would expect that when you get that far, you’ll be able to make the connection with how the block version is supposed to work, and why it’s able to do any number of different jobs depending on what block you give it. If not, I’ll be happy to answer any other questions you have (though off-list, probably, since this seems to be getting less and less general-interest). > Finding the longest or shortest string in an array is so trivial. > This really seems more like an exercise on howto structure blocks > and pass variables to methods. > > result = arr.sort\_by {|w| w.length}; > shortest,longest = result[0],result[-1] You’re exactly right. The point isn’t to teach you how to find the shortest or longest string in an array. It’s more to teach you how Ruby can use blocks, how the results of general methods can be altered depending on the block they’re passed, and how you might go about writing such a general method. Programming examples generally tend towards trivial, easily solved things with baroque restrictions on how to do them. Trivial examples are picked precisely _because_ they’re trivial - the student knows what needs to be done, and can easily see when you have the right answer and when you don’t. The restrictions are used to illustrate particular techniques and ways of thinking about problems in general. best of luck, matthew smillie. * * * Matthew S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Institute for Communicating and Collaborative Systems University of Edinburgh