Introspection in Ruby

Introduction#

What is introspection?

Introspection is looking inward to know about the inside. That is a simple definition of introspection.

In programming and Ruby in general…introspection is the ability to look at object, class… at run time to know about that one.

Lets see some examples

Example:

s = "Hello"  # s is a string

Then we find out something about s. Lets begin:

So you want to know what is the class of s at run time?

irb(main):055:0* s.class
=> String

Ohh, good. But what are the methods of s?

irb(main):002:0> s.methods
=> [:unicode_normalize, :include?, :to_c, :unicode_normalize!, :unicode_normalized?, :%, :*, :+, :count, :partition, :unpack, :encode, :encode!, :next, :casecmp, :insert, :bytesize, :match, :succ!, :next!, :upto, :index, :rindex, :replace, :clear, :chr, :+@, :-@, :setbyte, :getbyte, :<=>, :<<, :scrub, :scrub!, :byteslice, :==, :===, :dump, :=~, :downcase, :[], :[]=, :upcase, :downcase!, :capitalize, :swapcase, :upcase!, :oct, :empty?, :eql?, :hex, :chars, :split, :capitalize!, :swapcase!, :concat, :codepoints, :reverse, :lines, :bytes, :prepend, :scan, :ord, :reverse!, :center, :sub, :freeze, :inspect, :intern, :end_with?, :gsub, :chop, :crypt, :gsub!, :start_with?, :rstrip, :sub!, :ljust, :length, :size, :strip!, :succ, :rstrip!, :chomp, :strip, :rjust, :lstrip!, :tr!, :chomp!, :squeeze, :lstrip, :tr_s!, :to_str, :to_sym, :chop!, :each_byte, :each_char, :each_codepoint, :to_s, :to_i, :tr_s, :delete, :encoding, :force_encoding, :sum, :delete!, :squeeze!, :tr, :to_f, :valid_encoding?, :slice, :slice!, :rpartition, :each_line, :b, :ascii_only?, :hash, :to_r, :<, :>, :<=, :>=, :between?, :instance_of?, :public_send, :instance_variable_get, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :private_methods, :kind_of?, :instance_variables, :tap, :is_a?, :extend, :to_enum, :enum_for, :!~, :respond_to?, :display, :object_id, :send, :method, :public_method, :singleton_method, :define_singleton_method, :nil?, :class, :singleton_class, :clone, :dup, :itself, :taint, :tainted?, :untaint, :untrust, :trust, :untrusted?, :methods, :protected_methods, :frozen?, :public_methods, :singleton_methods, :!, :!=, :__send__, :equal?, :instance_eval, :instance_exec, :__id__]

You want to know if s is an instance of String?

irb(main):017:0*
irb(main):018:0* s.instance_of?(String)
=> true

What are the public methods of s?

irb(main):026:0* s.public_methods
=> [:unicode_normalize, :include?, :to_c, :unicode_normalize!, :unicode_normalized?, :%, :*, :+, :count, :partition, :unpack, :encode, :encode!, :next, :casecmp, :insert, :bytesize, :match, :succ!, :next!, :upto, :index, :rindex, :replace, :clear, :chr, :+@, :-@, :setbyte, :getbyte, :<=>, :<<, :scrub, :scrub!, :byteslice, :==, :===, :dump, :=~, :downcase, :[], :[]=, :upcase, :downcase!, :capitalize, :swapcase, :upcase!, :oct, :empty?, :eql?, :hex, :chars, :split, :capitalize!, :swapcase!, :concat, :codepoints, :reverse, :lines, :bytes, :prepend, :scan, :ord, :reverse!, :center, :sub, :freeze, :inspect, :intern, :end_with?, :gsub, :chop, :crypt, :gsub!, :start_with?, :rstrip, :sub!, :ljust, :length, :size, :strip!, :succ, :rstrip!, :chomp, :strip, :rjust, :lstrip!, :tr!, :chomp!, :squeeze, :lstrip, :tr_s!, :to_str, :to_sym, :chop!, :each_byte, :each_char, :each_codepoint, :to_s, :to_i, :tr_s, :delete, :encoding, :force_encoding, :sum, :delete!, :squeeze!, :tr, :to_f, :valid_encoding?, :slice, :slice!, :rpartition, :each_line, :b, :ascii_only?, :hash, :to_r, :<, :>, :<=, :>=, :between?, :pretty_print, :pretty_print_cycle, :pretty_print_instance_variables, :pretty_print_inspect, :instance_of?, :public_send, :instance_variable_get, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :private_methods, :kind_of?, :instance_variables, :tap, :pretty_inspect, :is_a?, :extend, :to_enum, :enum_for, :!~, :respond_to?, :display, :object_id, :send, :method, :public_method, :singleton_method, :define_singleton_method, :nil?, :class, :singleton_class, :clone, :dup, :itself, :taint, :tainted?, :untaint, :untrust, :trust, :untrusted?, :methods, :protected_methods, :frozen?, :public_methods, :singleton_methods, :!, :!=, :__send__, :equal?, :instance_eval, :instance_exec, :__id__]

and private methods…

irb(main):030:0* s.private_methods
=> [:initialize, :initialize_copy, :DelegateClass, :default_src_encoding, :irb_binding, :sprintf, :format, :Integer, :Float, :String, :Array, :Hash, :catch, :throw, :loop, :block_given?, :Complex, :set_trace_func, :trace_var, :untrace_var, :at_exit, :Rational, :caller, :caller_locations, :select, :test, :fork, :exit, :`, :gem_original_require, :sleep, :pp, :respond_to_missing?, :load, :exec, :exit!, :system, :spawn, :abort, :syscall, :printf, :open, :putc, :print, :readline, :puts, :p, :srand, :readlines, :gets, :rand, :proc, :lambda, :trap, :initialize_clone, :initialize_dup, :gem, :require, :require_relative, :autoload, :autoload?, :binding, :local_variables, :warn, :raise, :fail, :global_variables, :__method__, :__callee__, :__dir__, :eval, :iterator?, :method_missing, :singleton_method_added, :singleton_method_removed, :singleton_method_undefined]

Yes, do s have a method name upper. You want to get the upper case version of s? Lets try:

irb(main):044:0> s.respond_to?(:upper)
=> false

Look like not, the correct method is upcase lets check:

irb(main):047:0*
irb(main):048:0* s.respond_to?(:upcase)
=> true

Introspection of class

Lets following are the class definition

class A
   def a; end
end

module B
   def b; end
end

class C < A
   include B
   def c; end
end

What are the instance methods of C?

C.instance_methods # [:c, :b, :a, :to_json, :instance_of?...]

What are the instance methods that declare only on C?

C.instance_methods(false) # [:c]

What are the ancestors of class C?

C.ancestors # [C, B, A, Object,...]

Superclass of C?

C.superclass # A