class PP

A pretty-printer for Ruby objects.

What PP Does

Standard output by p returns this:

#<PP:0x81fedf0 @genspace=#<Proc:0x81feda0>, @group_queue=#<PrettyPrint::GroupQueue:0x81fed3c @queue=[[#<PrettyPrint::Group:0x81fed78 @breakables=[], @depth=0, @break=false>], []]>, @buffer=[], @newline="\n", @group_stack=[#<PrettyPrint::Group:0x81fed78 @breakables=[], @depth=0, @break=false>], @buffer_width=0, @indent=0, @maxwidth=79, @output_width=2, @output=#<IO:0x8114ee4>>

Pretty-printed output returns this:

    [[#<PrettyPrint::Group:0x81fed78 @break=false, @breakables=[], @depth=0>],
  [#<PrettyPrint::Group:0x81fed78 @break=false, @breakables=[], @depth=0>],


pp(obj)             #=> obj
pp obj              #=> obj
pp(obj1, obj2, ...) #=> [obj1, obj2, ...]
pp()                #=> nil

Output obj(s) to $> in pretty printed format.

It returns obj(s).

Output Customization

To define a customized pretty printing function for your classes, redefine method #pretty_print(pp) in the class.

#pretty_print takes the pp argument, which is an instance of the PP class. The method uses text, breakable, nest, group and pp to print the object.

Pretty-Print JSON

To pretty-print JSON refer to JSON#pretty_generate.


Tanaka Akira <>



Returns the sharing detection flag as a boolean value. It is false by default.

Public Class Methods

pp(obj, out=$>, width=79) click to toggle source

Outputs obj to out in pretty printed format of width columns in width.

If out is omitted, $> is assumed. If width is omitted, 79 is assumed.

::pp returns out.

# File lib/pp.rb, line 70
def PP.pp(obj, out=$>, width=79)
  q =, width)
  q.guard_inspect_key {q.pp obj}
  #$pp = q
  out << "\n"
singleline_pp(obj, out=$>) click to toggle source

Outputs obj to out like ::pp but with no indent and newline.

::singleline_pp returns out.

# File lib/pp.rb, line 82
def PP.singleline_pp(obj, out=$>)
  q =
  q.guard_inspect_key {q.pp obj}