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Closed 11 years ago.
Here's what I am trying to do: The user enters a string. The string contains 2 parts and will look like this:
{EventClass: someMethod=>arg1, arg2, arg3....}, {Action: someMethod=>arg1, arg2, arg3....}
A concrete example of this would be:
{TwitterEvent: newTweet=>arg1, arg2, arg3....}, {PersistenceAction: saveToHardDrive=>arg1 arg2...}
Then I will parse this string, instantiate an instance of TwitterEvent, call that method on it. Then do the same thing for PersistenceAction
What the best "design" for this type of application? How would I dynamically instantiate classes from parsed string and then call method? And potentially, the method will have arguments? How would I detect/handle errors?
Get class object from name string:
Kernel.const_get('TwitterEvent')
Invoke arbitrary method on object:
event.send(:new_tweet)
The rest is up to you. :-)
You want to use respond_to? and send . Send allows you to invoke a method using a symbol. You can use to_sym to convert a string to a symbol.
Here you go
str = "{TwitterEvent: newTweet=>arg1, arg2, arg3}, {PersistenceAction: saveToHardDrive=>arg1, arg2}"
regexp = /^{(\w+):\s*(\w+)=>([^}]+)},\s*{(\w+):\s*(\w+)=>([^}]+)}$/
regexp.match(str).to_a[1..-1].each_slice(3) do |s|
# s[0] .. class name
# s[1] .. class method
# s[2] .. method parameters as a single string
# do something similar to Sergio Tulentsev suggestion
end
Related
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Closed 9 years ago.
Lets say,
script = Array.new
script.push("/home/dexter/constant.sh")
script.push("/home/dexter/constant_validation.rb")
script.push("/home/dexter/jobs/reporter.rb")
Now when I use array's delete_if method,
script.compact.delete_if {|s| s =~ /constant/}
This should remove elements from array containing "constant". This is the output I get when i perform it under interactive ruby.
puts script => ["/home/dexter/jobs/reporter.rb"]
I am pushing the elements into the array with the help of regular expression matching.
Any ideas what am I doing wrong?
Cheers.
While delete_if is destructive and work on the message receiver, since you use compact method which returns different instance from self, the instance you send delete_if message to, is different from the script.
So, you will get desired result if you run script.compact! then script.delete_if.
There is no delete_if! since delete_if itself modify self.
script = Array.new
script.push("/home/dexter/constant.sh")
script.push("/home/dexter/constant_validation.rb")
script.push("/home/dexter/jobs/reporter.rb")
script
#=> ["/home/dexter/constant.sh",
"/home/dexter/constant_validation.rb",
"/home/dexter/jobs/reporter.rb"]
As #shigeya said above, compact returns different instance of self. You can verify that as:
script.object_id
#=>72421740
script.compact.object_id
#=> 71512710
Thus, by using compact in chain with delete_if, you are making changes on the object array returned by script.compact and not script itself,
`delete_if` **will** destruct the calling array
script.delete_if { |s| s =~ /constant/ }
=> ["/home/dexter/jobs/reporter.rb"]
script
=> ["/home/dexter/jobs/reporter.rb"]
Ok.. so the mistake i was doing in the script was,
I was adding elements into the script array in my script with the help of regular expressions.
So when I did a class check on the elements of the array i found that they were of type "MatchData" and hence the delete_if was not working.
If you want to do it in one line it would need to look like:
script.tap{|s| s.compact}.delete_if {|s| s =~ /constant/}
Otherwise your changes won't affect script.
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Closed 9 years ago.
Does polymorphism exist in Ruby? I've read that Ruby does not support polymorphism, and instead it supports method overloading and method overriding. Can someone clarify this for me with an example?
Yes, Ruby does support polymorphism.
Consider the case of simple class inheritance where an instance of a derived class "is a" instance of both the child and parent classes:
class Parent; end
class Child < Parent; end
o = Child.new
o.is_a?(Child) # => true
o.is_a?(Parent) # => true
Note that this example is also valid for included modules:
a = Array.new
a.is_a?(Array) # => true
a.is_a?(Enumerable) # => true
Of course, Ruby also encourages duck typing, which may be the source of confusion regarding the question of properly supporting polymorphism.
Ruby is a highly polymorfic language, in the sense methods don't automatically infer what data type you are passing to them, as long as the object behaves like expected. Example:
def concat(a,b)
a.to_s + b.to_s
end
concat('a', 'bcd') #=> "abcd"
concat(5, 10) #=> "510"
concat([1,2,3], ' is an Array') #=> "[1, 2, 3] is an Array"
As long as a and b respond to to_s, the function will output as expected. Check more about Duck Typing for examples.
Ruby doesn't support method overloading. The very idea of method overloading doesn't even make sense in a dynamically typed language.
Ruby does support ad-hoc polymorphism, just like pretty much every object-oriented language on the planet.
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Closed 10 years ago.
I have the following code:
def test_compare()
if true
condition = true
else
condition = false
end
assert_equal(true, condition)
end
In Ruby, variables inside of an if block have the same scope as variables declared outside of the if block according to "I don't understand ruby local scope".
Is it common practice to initialize variables inside of a control structure without first declaring them or initializing them outside of a control structure?
Coming from a Java.NET background this seems to make the code less readable and more prone to logic mistakes.
I am doing my best to "not write .NET code in Ruby", but want to understand why the above makes more sense than declaring scope variables at the beginning of the scope, or outside of the control structure.
if returns value. It's cleaner to use this behaviour.
x = if condition
# several lines of calculations can be here
'true value'
else
# several lines of calculations can be here
'false value'
end
Or, in this concrete case it's better to use ternary operator. It does the same thing and is shorter.
x = condition ? 'true value' : 'false value'
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Closed 10 years ago.
I would like to write a simple documentation generator in ruby that will take a standard .rb file and list all of the classes or modules defined, all of the methods and variables defined in each class or module, and indicate whether any methods are aliased or inherited from a super class.
How should I approach this?
Reverse-engineering YARD is probably the best idea (not sure why it's a comment). Alternatively, you could probably do this with the ruby_parser gem.
require 'ruby_parser'
class SillyRubyParserExample
def self.example
class_eval(RubyParser.new.parse(<<-EOS
class ParseMe
def a() end
def b() end
end
EOS
).inspect)
end
def self.s(*args)
if args[0] == :defn
puts "def " + args[1].to_s
elsif args[0] == :class
puts "class " + args[1].to_s
end
end
end
SillyRubyParserExample.example
Produces:
def a
def b
class ParseMe
Of course, this is just a silly example, merely listing methods and classes.
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Closed 10 years ago.
So I want to be able to define a class like this:
class MyHouse < Home
things :bed, :lamp, :chair
end
Where Home takes care of putting those "things" in an array, like this:
class Home
attr_accessor :things
def things(*things)
#things = []
things.each { |thing| #things << thing }
end
end
The problem with this is I get:
NoMethodError: undefined method `things' for MyHouse:Class
I know there's a way to do this. Help appreciated,
Thanks,
Pachun
def things should be def self.things
That makes it a class method rather than an instance method.