mruby-metaprog: add README.md

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mrbgems/mruby-metaprog/README.md

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+# mruby-metaprog
+
+This mrbgem provides a collection of methods for metaprogramming in mruby. Metaprogramming is the ability of a program to inspect, modify, and create its own code at runtime.
+
+## Functionality
+
+The `mruby-metaprog` mrbgem offers methods for:
+
+- **Instance Variable Manipulation:**
+  - `instance_variable_defined?(symbol)`: Checks if an instance variable is defined in an object.
+  - `instance_variable_get(symbol)`: Retrieves the value of an instance variable.
+  - `instance_variable_set(symbol, value)`: Sets the value of an instance variable.
+  - `instance_variables()`: Returns an array of instance variable names in an object.
+- **Method Inspection:**
+  - `methods(regular=true)`: Returns a list of public and protected methods of an object.
+  - `private_methods(all=true)`: Returns a list of private methods accessible to an object.
+  - `protected_methods(all=true)`: Returns a list of protected methods accessible to an object.
+  - `public_methods(all=true)`: Returns a list of public methods accessible to an object.
+  - `singleton_methods(all=true)`: Returns an array of singleton method names for an object.
+- **Singleton Method Definition:**
+  - `define_singleton_method(name, &block)`: Defines a singleton method for an object.
+- **Class Variable Manipulation:**
+  - `class_variable_defined?(symbol)`: Checks if a class variable is defined in a module.
+  - `class_variable_get(symbol)`: Retrieves the value of a class variable.
+  - `class_variable_set(symbol, value)`: Sets the value of a class variable.
+  - `class_variables(inherit=true)`: Returns an array of class variable names in a module.
+  - `remove_class_variable(symbol)`: Removes a class variable from a module.
+- **Module Inspection:**
+  - `included_modules()`: Returns a list of modules included in a module or class.
+  - `instance_methods(include_super=true)`: Returns an array of public and protected instance methods in a module or class.
+  - `public_instance_methods(include_super=true)`: Returns an array of public instance methods in a module or class.
+  - `private_instance_methods(include_super=true)`: Returns an array of private instance methods in a module or class.
+  - `protected_instance_methods(include_super=true)`: Returns an array of protected instance methods in a module or class.
+  - `undefined_instance_methods()`: Returns an array of undefined instance methods in a module/class.
+- **Method Removal:**
+  - `remove_method(symbol)`: Removes a method from a class.
+- **Constant Inspection:**
+  - `constants(inherit=true)`: Returns an array of constant names defined in a module.
+- **Module Nesting:**
+  - `Module.nesting()`: Returns an array representing the current module nesting.
+- **Message Sending:**
+  - `send(symbol, *args, &block)`: Invokes a method on an object.
+  - `public_send(symbol, *args, &block)`: Invokes a public method on an object.
+- **Variable Inspection:**
+  - `global_variables()`: Returns an array of global variable names.
+  - `local_variables()`: Returns an array of local variable names in the current scope.
+
+## Examples
+
+### Working with Instance Variables
+
+```ruby
+class MyClass
+  def initialize(value)
+    @my_var = value
+  end
+end
+
+obj = MyClass.new(10)
+
+p obj.instance_variable_defined?(:@my_var)  #=> true
+p obj.instance_variable_get(:@my_var)     #=> 10
+obj.instance_variable_set(:@another_var, "hello")
+p obj.instance_variables                   #=> [:@my_var, :@another_var]
+```
+
+### Inspecting Methods
+
+```ruby
+class AnotherClass
+  def public_method; end
+  protected
+  def protected_method; end
+  private
+  def private_method; end
+end
+
+obj = AnotherClass.new
+p obj.public_methods(false)    #=> [:public_method]
+p obj.protected_methods(false) #=> [:protected_method]
+p obj.private_methods(false)   #=> [:private_method]
+
+def obj.singleton_method_example; end
+p obj.singleton_methods        #=> [:singleton_method_example]
+```
+
+### Defining Singleton Methods
+
+```ruby
+obj = Object.new
+obj.define_singleton_method(:greet) do |name|
+  "Hello, #{name}!"
+end
+p obj.greet("World")  #=> "Hello, World!"
+```
+
+### Working with Class Variables
+
+```ruby
+class ParentClass
+  @@parent_cvar = 100
+end
+
+class ChildClass < ParentClass
+  @@child_cvar = 200
+
+  def self.get_parent_cvar
+    class_variable_get(:@@parent_cvar)
+  end
+end
+
+p ChildClass.class_variable_defined?(:@@child_cvar)  #=> true
+p ChildClass.class_variable_get(:@@child_cvar)     #=> 200
+ChildClass.class_variable_set(:@@new_cvar, 300)
+p ChildClass.class_variables.sort                   #=> [:@@child_cvar, :@@new_cvar, :@@parent_cvar] (order may vary)
+p ChildClass.get_parent_cvar                        #=> 100
+ChildClass.remove_class_variable(:@@new_cvar)
+p ChildClass.class_variables.sort                   #=> [:@@child_cvar, :@@parent_cvar] (order may vary)
+```
+
+## License
+
+This mrbgem is licensed under the [MIT License](LICENSE).