Ruby の定番対話ツール pry 徹底攻略 | Special Locals

概要

Ruby の定番対話ツール pry 徹底攻略
Special Locals について

Special Locals

Pry はセッションにいくつかのローカル変数を注入します。
それは、 irb で最後に実行された変数を参照する _ に似ています。

Special Local の役割は、プログラマにとって役に立つ便利な情報を
効率よく取得できるようにすることです。

Last result

local name: `_`

local 変数 _ は最後に評価された値を保持します。
; を利用して標準出力を抑止した場合にも変数の値は更新されます。

[4] pry(main)> "hoge"*3
=> "hogehogehoge"
[5] pry(main)> _
=> "hogehogehoge"
[6] pry(main)> "hoge".chars;
[7] pry(main)> _
=>

Last exception

local name: `_ex_`

local 変数 _ex_ は最後に発生した例外を保持します。
; を利用して標準出力を抑止した場合にも変数の値は更新されます。

[11] pry(main)> "hoge".to_hoge
NoMethodError: undefined method `to_hoge' for "hoge":String
from (pry):6:in `__pry__'
[12] pry(main)> _ex_
=> #<NoMethodError: undefined method `to_hoge' for "hoge":String>
[18] pry(main)> _ex_.backtrace.size
=> 28
[19] pry(main)> _ex_.backtrace.first(3)
=> ["(pry):9:in `__pry__'",
 "/home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:355:in `eval'",
 "/home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:355:in `evaluate_ruby'"]

`wtf?` command

例外の backtrance の表示には wtf? コマンドも利用できます。
デフォルトで 10 行。
メソッド名の後に続けて ! か ? をつけるたびに追加で 10 行出力するという謎インターフェース。

wtf? 試用

[11] pry(main)> "hoge".to_hoge
[23] pry(main)> wtf?
Exception: NoMethodError: undefined method `to_hoge' for "hoge":String
--
0: (pry):9:in `__pry__'
1: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:355:in `eval'
2: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:355:in `evaluate_ruby'
3: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:323:in `handle_line'
4: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:243:in `block (2 levels) in eval'
5: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:242:in `catch'
6: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:242:in `block in eval'
7: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:241:in `catch'
8: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:241:in `eval'
9: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/repl.rb:77:in `block in repl'

[42] pry(main)> wtf?!?
Exception: NoMethodError: undefined method `to_hoge' for "hoge":String
--
 0: (pry):9:in `__pry__'
 1: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:355:in `eval'
 2: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:355:in `evaluate_ruby'
 3: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:323:in `handle_line'
 4: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:243:in `block (2 levels) in eval'
 5: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:242:in `catch'
 6: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:242:in `block in eval'
 7: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:241:in `catch'
 8: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_instance.rb:241:in `eval'
 9: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/repl.rb:77:in `block in repl'
10: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/repl.rb:67:in `loop'
11: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/repl.rb:67:in `repl'
12: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/repl.rb:38:in `block in start'
13: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/input_lock.rb:61:in `call'
14: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/input_lock.rb:61:in `__with_ownership'
15: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/input_lock.rb:79:in `with_ownership'
16: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/repl.rb:38:in `start'
17: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/repl.rb:15:in `start'
18: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/pry_class.rb:169:in `start'
19: /home/path/to/ruby/gems/2.0.0/gems/pry-debugger-0.2.3/lib/pry-debugger/pry_ext.rb:19:in `start_with_pry_debugger'
20: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/cli.rb:219:in `block in <top (required)>'
21: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/cli.rb:83:in `call'
22: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/cli.rb:83:in `block in parse_options'
23: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/cli.rb:83:in `each'
24: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/cli.rb:83:in `parse_options'
25: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/bin/pry:16:in `<top (required)>'
26: /home/path/to/ruby/2.0.0-p0/bin/pry:23:in `load'
27: /home/path/to/ruby/2.0.0-p0/bin/pry:23:in `<main>'

wtf? ドキュメント

[38] pry(main)> show-doc wtf?

From: /home/path/to/ruby/gems/2.0.0/gems/pry-0.10.1/lib/pry/commands/wtf.rb 
Number of lines: 14

Usage: wtf[?|!]

Show's a few lines of the backtrace of the most recent exception (also available
as `_ex_.backtrace`). If you want to see more lines, add more question marks or
exclamation marks.

wtf?
wtf?!???!?!?

# To see the entire backtrace, pass the `-v` or `--verbose` flag.
wtf -v

    -v, --verbose      Show the full backtrace
    -h, --help         Show this message.

`cat --ex`

cat --ex でエラーが発生した行をシンタックスハイライト付きで表示します。

The input and output cache

local names: `_in_` と `_out_`

_in_ と _out_ は入力（コードの評価内容）と出力の履歴を保持します。
純粋な Ruby のコードのみを保持し、 Pry のコードは保持しません。

[84] pry(main)> hoge = 3
=> 3
[85] pry(main)> "hige".upcase
=> "HIGE"
[86] pry(main)> "hage".capitalize
=> "Hage"
[87] pry(main)> _in_.to_a.last(3)
=> ["hoge = 3\n", "\"hige\".upcase\n", "\"hage\".capitalize\n"]
[88] pry(main)> _out_.to_a.last(3)
=> ["HIGE",
 "Hage",
 ["hoge = 3\n", "\"hige\".upcase\n", "\"hage\".capitalize\n"]]

`_in_` と `_out_` のメモリサイズ

Pry.config.memory_size で設定します。

Last file, and last directory

local names: `_file_` and `_dir_`

show-method, show-doc, show-source, stat and cat などのコマンドを実行した際に
_file_ and _dir_ の値が更新されます。
_file_ はファイル名。
_dir_ はディレクトリ名。

$ pry
[1] pry(main)> require 'prime'
=> true
[2] pry(main)> _file_
=> nil
[3] pry(main)> _dir_
=> nil
[4] pry(main)> show-method Prime.ins
Prime.inspect                     Prime.instance_of?
Prime.instance                    Prime.instance_variable_defined?
Prime.instance_eval               Prime.instance_variable_get
Prime.instance_exec               Prime.instance_variable_set
Prime.instance_method             Prime.instance_variables
Prime.instance_methods            
[4] pry(main)> show-method Prime.instance

From: /home/path/to/ruby/2.0.0/prime.rb @ line 106:
Owner: #<Class:Prime>
Visibility: public
Number of lines: 1

def instance; @the_instance end
[5] pry(main)> _file_
=> "/home/path/to/ruby/2.0.0/prime.rb"
[6] pry(main)> _dir_
=> "/home/path/to/ruby/2.0.0"