from actual parameter of type array to formal parameter of list in Ruby

I was curious what * (star) means in front of a method parameter. Here is the result:

def xyz(*arr)
arr.each do |a|
puts a.class
end
end

$xyz 1,2,3
=> Fixnum, Fixnum, Fixnum
$xyz [1,2,3]
=> Array
$xyz *[1,2,3]
=> Fixnum, Fixnum, Fixnum

Therefore, for example,

attribute_names = 'name', 'age', 'phone_number' #creates an array
attr_accessor *attribute_names

is equivalent to

attr_accessor 'name', 'age', 'phone_number'

Comments

Post a Comment

Popular posts from this blog

Creating an HTTP Streaming Client in Silverlight

I read and played with WebClient and HttpWebRequest classes. Both of these classes allow you to make requests to an http server. Once you make the request, you give a callback that is invoked once the response is received so you can happily examine the response. Let's say your HTTP server is streaming a file, or it wants to hold on to your request and sends messages as necessary from the same connection. To be able to work with such a server, your http client must be able to read the data as soon as it is available without requiring the response to be received completely.  After searching silverlight forums I found a solution. The solution assumes that you have a control on the server code or the response you are getting is bigger than 4KB (IE buffers upto 4KB). Here is the code snipped for your client side: HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri); request.Method = "POST"; request.AllowReadStreamBuffering = false; try {  request.BeginGetResponse(On...
Read more

The Order of Rails Validation Filters

Here are the available Rails validation filters: before_validation_on_update before_validation_on_create validate validate_on_update validate_on_create after_validation after_validation_on_update after_validation_on_create before_save before_update before_create after_update after_create after_save These filters are callbacks that are invoked automatically. The difference between update and create is really with respect to the database. If the record you are saving is a new record in the db, then it means you are creating. If the item already exists but you are making a change, then it means you are updating. In other words, it does not matter, whether you called obj.save or obj.create, before_update filter will be invoked. The same is true for obj.save vs. obj.update_attributes. So no matter what Active record method you invoke the filter is decided based on the database record. How about before_save, before_after_save? They will always be invoked whether you are creating or updating....
Read more

Comparison of equality operators in Ruby: == vs. equal? vs. eql? vs. ===

Here is a short explanation of when these predicates are true (From http://www.wellho.net/mouth/985_Equality-in-Ruby-eql-and-equal-.html) The == comparison checks whether two values are equal eql? checks if two values are equal and of the same type equal? checks if two things are one and the same object. How do I remember which is which ... The longer the operator, the more restrictive the test it performs Let's understand the differences with some examples. Each "abc" below is a different object. Therefore, equal? is false. irb(main):065:0> "abc".object_id => 24173330 irb(main):066:0> "abc".object_id => 24165760 irb(main):067:0> "abc" == "abc" => true irb(main):068:0> "abc".eql? "abc" => true irb(main):069:0> "abc".equal? "abc" => false As you might expect, there is a single instance of 1. Therefore, all comparisons are true. irb(main):094:0> 1.class =>...
Read more