idioms

What C++ idioms should C++ programmers know? By C++ idioms, I mean design patterns or way of doing certain things that are only applicable for C++ or more applicable for C++ than most other languages. Why one should use the idioms, and what do the idioms accomplish? Here is one list . If I had to pick a couple I might go with the Curiously Recurring Template Pattern or Virtual Contstructors. By far the single most important "pattern" to learn and know that's (nearly) unique to C++ is RAII (Resource Acquisition Is Initialization). Edit: (To answer extra question edited into the question). You

I've been using ((:[]) <$> xs) but if there is a more clear way I would love to use it. edit: so many good answers guys! I don't think I can accept one because they are all good. I believe map return or map pure are good enough. Maybe this? map (\x -> [x]) xs Yours can work on any functor I think so this would be more idomatic for just lists. The split package provides a (Data.List.Split.)chunksOf function whose name is, IMO, more meaningful than the various map solutions (even if they are more idiomatic.) You can also use a list comprehension: [ [x] | x <- theList] Maybe overkill for such a

Let's say that you have a function like this: func getSomething(error: NSErrorPointer) -> Something and you typically use it this way: var error : NSError? = nil let a = getSomething(&error) What is an idiomatic way to check for error here? More specific questions: If error == nil can we assume that a will never be nil and vice versa? What should we check first: error (for its nilness) or a (to confirm that it's not a nil)? Can a != nil && error != nil be true in some cases? Thank you! Compare Handling Error Objects Returned From Methods in the "Error Handling Programming Guide": Important:

What is the preferred method of using std::rel_ops to add the full set of relational operators to a class? This documentation suggests a using namespace std::rel_ops , but this seems to be deeply flawed, as it would mean that including the header for the class implemented in this way would also add full relational operators to all other classes with a defined operator< and operator== , even if that was not desired. This has the potential to change the meaning of code in surprising ways. As a side note - I have been using Boost.Operators to do this, but I am still curious about the standard

I'm trying to make an API for my rails application using JSON responses to RESTful resource controllers. This is a new experience for me, so I'm looking for some guidance and pointers. To start things off: In a rails application, what is the "proper" way to respond with JSON to REST-ful controller methods? (create, update, destroy) Is there an idiomatic way to indicate success/failure through a JSON response? Additional information: I'm currently working with rails 3.0.beta2 I would like to avoid using a plugin or gem to do the grunt work, my goal is to gain a better understanding of how to

I have a standard many-to-many relationship between users and roles in my Rails app: class User < ActiveRecord::Base has_many :user_roles has_many :roles, :through => :user_roles end I want to make sure that a user can only be assigned any role once. Any attempt to insert a duplicate should ignore the request, not throw an error or cause validation failure. What I really want to represent is a "set", where inserting an element that already exists in the set has no effect. {1,2,3} U {1} = {1,2,3}, not {1,1,2,3}. I realize that I can do it like this: user.roles << role unless user.roles.include?

One thing I love about ruby is that mostly it is a very readable language (which is great for self-documenting code) However, inspired by this question: Ruby Code explained and the description of how ||= works in ruby, I was thinking about the ruby idioms I don't use, as frankly, I don't fully grok them. So my question is, similar to the example from the referenced question, what common, but not obvious, ruby idioms do I need to be aware of to be a truly proficient ruby programmer? By the way, from the referenced question a ||= b is equivalent to if a == nil || a == false a = b end (Thanks to