---
layout: post
title:  "Every day learing"
date:   2016-01-14
categories: learning
---


<b>Ghost Methods</b>
<p>
  From the caller’s side, a message that’s processed by method_missing looks like
a regular call—but on the receiver’s side, it has no corresponding method.
This trick is called a Ghost Method.
</p>
<b>Dynamic Proxies</b>
<p>
  When an object(wrapper object that contain other object) receive ghost method call and simply use that call to
  get data from contained object is called Dynamic Proxies.
</p>

<P>
  Every time we override method_missing(for use ghost method) we should also override respond_to_missing?
  Because ghost method call on respond_to? will not respond.
</P>
<b>module const_missing method</b>
<p>
  When you reference a constant that doesn’t exist, Ruby passes the name of
the constant to const_missing as a symbol. Class names are just constants
</p>
<p>N.B: When we use ghost method need to extra carefull because it may cause infinity call</p>
<ul>There are exactly three places where a program leaves the previous scope
behind and opens a new one:
  <li>Class definitions</li>
  <li>Class definitions</li>
  <li>Class definitions</li>
</ul>
<p>Ruby class is not special thing it just give us new scope</p>
<b>Solve Rubymine keyboard freez problem</b>
Keyboard input may be unlocked by restarting IBus daemon from a console:

<code>ibus-daemon -rd</code>
IBus can be disabled for IDEA by unsetting env. variable XMODIFIERS, but ability to input national characters in IDEA will be lost:

<code>XMODIFIERS="" idea.sh</code>
I have used the second one and fixed my problem.

<p>@indicate inctace objecct of self. If during declaretoin of @var self is class then it class es instace objeect, if 
self indicate obje then it object's instance variable.</p>

<p>Like other programming language, ruby instance variable is not open to out side world(class).{In java public inctance 
variable is accessabe using dot(.) operator outside of class}So, to access variable we have to declare getter/setter method
in ruby.(There are many way to access variable in ruby like instace_variable_get, instacnce_eval, eval</p>
<p>We can make flat scope for sharing local variable between two or more methods</p>
<ul>Different way make flat scope in ruby
<li>
  user <code>var = 1, obj.instance_exec(var) {|var| var }</code> where we pass var local's to boj scope
</li>
<li>
  <code>Class.new(var)/Module.new(var)</code>passing var to class & module scope.
</li>
<li>
  
</li>
</ul>
<p>Example of flat scope
  <code>my_var = "Success"
 
MyClass = Class.new do
    "#{my_var} in the class definition"
 
    # Have to use dynamic method creation to access my_var
    define_method :my_method do
        "#{my_var} in the method"
    end
end
 
puts MyClass.new.my_method
 
# => Success in the method</code></p>



<p><h2>Difference between undef_method and remove_method in ruby</h2></p>
You can remove a method in two easy ways. The drastic

Module#undef_method( ) 
removes all methods, including the inherited ones. The kinder

Module#remove_method( ) 
removes the method from the receiver, but it leaves inherited methods alone.

See below 2 simple example -

Example 1 using undef_method

class A 
    def x
        puts "x from A class"
    end
end

class B < A
    def x
        puts "x from B Class"
    end
    undef_method :x
end

obj = B.new
obj.x
result - main.rb:15:in 
': undefined methodx' for # (NoMethodError)

Example 2 using remove_method

class A 
    def x
        puts "x from A class"
    end
end

class B < A
    def x
        puts "x from B Class"
    end
    remove_method :x
end

obj = B.new
obj.x
Result - $ruby main.rb

x from A class
<h3> Issues using div with in `a` tag</h3>
<p>Normally div with in a tag is not allowed. If we need apply display: display on a tag. Again we are not able to use
a tag with in a tag. </p>