Most objects are cloneable, but not all. For example you can‘t dup nil:
nil.dup # => TypeError: can't dup NilClass
Classes may signal their instances are not duplicable removing dup/clone or raising exceptions from them. So, to dup an arbitrary object you normally use an optimistic approach and are ready to catch an exception, say:
arbitrary_object.dup rescue object
Rails dups objects in a few critical spots where they are not that arbitrary. That rescue is very expensive (like 40 times slower than a predicate), and it is often triggered.
That‘s why we hardcode the following cases and check duplicable? instead of using that rescue idiom.
__send__ | -> | try |
A duck-type assistant method. For example, Active Support extends Date to define an acts_like_date? method, and extends Time to define acts_like_time?. As a result, we can do "x.acts_like?(:time)" and "x.acts_like?(:date)" to do duck-type-safe comparisons, since classes that we want to act like Time simply need to define an acts_like_time? method.
An object is blank if it‘s false, empty, or a whitespace string. For example, "", " ", nil, [], and {} are blank.
This simplifies:
if !address.nil? && !address.empty?
…to:
if !address.blank?
Can you safely .dup this object? False for nil, false, true, symbols, numbers, class and module objects; true otherwise.
Returns object if it‘s present? otherwise returns nil. object.presence is equivalent to object.present? ? object : nil.
This is handy for any representation of objects where blank is the same as not present at all. For example, this simplifies a common check for HTTP POST/query parameters:
state = params[:state] if params[:state].present? country = params[:country] if params[:country].present? region = state || country || 'US'
…becomes:
region = params[:state].presence || params[:country].presence || 'US'
Returns value after yielding value to the block. This simplifies the process of constructing an object, performing work on the object, and then returning the object from a method. It is a Ruby-ized realization of the K combinator, courtesy of Mikael Brockman.
# Without returning def foo values = [] values << "bar" values << "baz" return values end foo # => ['bar', 'baz'] # returning with a local variable def foo returning values = [] do values << 'bar' values << 'baz' end end foo # => ['bar', 'baz'] # returning with a block argument def foo returning [] do |values| values << 'bar' values << 'baz' end end foo # => ['bar', 'baz']
Converts an object into a string suitable for use as a URL query string, using the given key as the param name.
Note: This method is defined as a default implementation for all Objects for Hash#to_query to work.
Invokes the method identified by the symbol method, passing it any arguments and/or the block specified, just like the regular Ruby Object#send does.
Unlike that method however, a NoMethodError exception will not be raised and nil will be returned instead, if the receiving object is a nil object or NilClass.
Without try
@person && @person.name
or
@person ? @person.name : nil
With try
@person.try(:name)
try also accepts arguments and/or a block, for the method it is trying
Person.try(:find, 1) @people.try(:collect) {|p| p.name}
An elegant way to factor duplication out of options passed to a series of method calls. Each method called in the block, with the block variable as the receiver, will have its options merged with the default options hash provided. Each method called on the block variable must take an options hash as its final argument.
with_options :order => 'created_at', :class_name => 'Comment' do |post| post.has_many :comments, :conditions => ['approved = ?', true], :dependent => :delete_all post.has_many :unapproved_comments, :conditions => ['approved = ?', false] post.has_many :all_comments end
Can also be used with an explicit receiver:
map.with_options :controller => "people" do |people| people.connect "/people", :action => "index" people.connect "/people/:id", :action => "show" end