Procを制する者がRubyを制す(嘘)

def square(n)
 n * n
end
sq = square # squareメソッドを変数sqに代入してみる
# ~> -:1:in `square': wrong number of arguments (0 for 1) (ArgumentError)
# ~> 	from -:5:in `<main>'

def square(n)
 n * n
end
def print_func(arg, fun)
 puts fun(arg)
end
print_func(4, square) # squareメソッドを引数として渡してみる
# ~> -:1:in `square': wrong number of arguments (0 for 1) (ArgumentError)
# ~> 	from -:9:in `<main>'

def square(n)
 n * n
end
sq = method(:square) # squareメソッドをオブジェクト化して変数sqに代入
sq # => #<Method: Object#square>

sq = method(:square)
sq(3) # 括弧で引数を渡して呼んでみる
# ~> -:7:in `<main>': undefined method `sq' for main:Object (NoMethodError)

def square(n)
 n * n
end
sq = method(:square)
sq.call(3) # => 9
def print_func(arg, fun)
 puts fun.call(arg)
end
print_func(4, sq)
# >> 16

sq = method(:square)
sq[3] # => 9
sq.(3) # => 9

def print_func(arg, &fun)
 puts fun.call(arg)
end
print_func(4) { |n| n * n }
# >> 16

def print_func(arg)
 puts yield(arg)
end
print_func(4) { |n| n * n }
# >> 16

lambda { |n| n * n } # => #<Proc:0x007f89a1852960@-:13 (lambda)>
proc { |n| n * n } # => #<Proc:0x007f89a18526b8@-:14>
Proc.new { |n| n * n } # => #<Proc:0x007f89a1852438@-:15>
->n{ n * n } # => #<Proc:0x007f89a1852190@-:16 (lambda)>

square = ->n{ n * n }
square.call(3) # => 9
def print_func(arg, fun)
 puts fun.call(arg)
end
print_func(4, square) 
# >> 16

def print_func(arg, fun)
 puts fun.call(arg)
end
print_func(4, ->n{ n * n }) 
# >> 16

def print_func(arg, &fun)
 puts fun.call(arg)
end
print_func(4) { |n| n * n }
# >> 16

def print_func(arg, &fun)
+ puts fun.class
end
print_func(4) { |n| n * n }
# >> Proc

def print_func(arg, &fun)
 puts fun.call(arg)
end
print_func(4, &3)
# ~> -:22:in `<main>': wrong argument type Fixnum (expected Proc) (TypeError)

class Fixnum
 def to_proc
 ->n{ self ** n }
 end
end
def print_func(arg, &fun)
 puts fun.call(arg)
end
print_func(4, &3)
# >> 81

def square(n)
 n * n
end
sq = method(:square)
def print_func(arg, &fun)
 puts fun.call(arg)
end
print_func(4, &sq)
# >> 16

%w(charlie liz george).map(&:capitalize) # => ["Charlie", "Liz", "George"]
require "prime"
(1..50).select(&:prime?) # => [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

%w(charlie liz george).map { |name| name.capitalize } # => ["Charlie", "Liz", "George"]
(1..50).select { |i| i.prime? } # => [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

pry(main)> show-source Symbol#to_proc
From: string.c (C Method):
Owner: Symbol
Visibility: public
Number of lines: 29
static VALUE
sym_to_proc(VALUE sym)
{
 static VALUE sym_proc_cache = Qfalse;
 enum {SYM_PROC_CACHE_SIZE = 67};
 VALUE proc;
 long id, index;
 VALUE *aryp;
 if (!sym_proc_cache) {
 sym_proc_cache = rb_ary_tmp_new(SYM_PROC_CACHE_SIZE * 2);
 rb_gc_register_mark_object(sym_proc_cache);
 rb_ary_store(sym_proc_cache, SYM_PROC_CACHE_SIZE*2 - 1, Qnil);
 }
 id = SYM2ID(sym);
 index = (id % SYM_PROC_CACHE_SIZE) << 1;
 aryp = RARRAY_PTR(sym_proc_cache);
 if (aryp[index] == sym) {
 return aryp[index + 1];
 }
 else {
 proc = rb_proc_new(sym_call, (VALUE)id);
 aryp[index] = sym;
 aryp[index + 1] = proc;
 return proc;
 }
}

class Symbol
 def to_proc
 sym = self
 Proc.new do |*args, &b|
 raise ArgumentError, "no receiver given" if args.empty?
 args.shift.__send__(sym, *args, &b)
 end
 end
end

class String
 def to_proc
 ->obj{ obj.send(self) }
 end
end
%w(charlie liz george).map(&'capitalize') # => ["Charlie", "Liz", "George"]
require "prime"
(1..50).select(&'prime?') # => [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]

:**.to_proc[2, 8] # => 256
:+.to_proc['ruby', 'ist'] # => "rubyist"
:grep.to_proc[['hello', 'world', 'ruby'], /ll/] # => ["hello"]

class X
 n = 2
 %w(a b c).each do |name|
 define_method(name) do
 n += 1
 end
 end
end

x = X.new
x.a # => 3
x.b # => 4
x.c # => 5
x.a # => 6
x.b # => 7
x2 = X.new
x2.a # => 8
x2.b # => 9
x2.c # => 10

class X
 n = 2
 %w(a b c).each do |name|
 define_method(name) do
 n += 1
 end
 end
 n = 10
end
x = X.new
x.a # => 11
x.b # => 12
x.c # => 13
x.a # => 14
x.b # => 15
x2 = X.new
x2.a # => 16
x2.b # => 17
x2.c # => 18

def join_ist(body)
 body + 'ist'
end
def join_er(body)
 body + 'er'
end
def join_ian(body)
 body + 'ian'
end

def join(suffix, body)
 body + suffix
end
def join_ist(body)
 join('ist', body)
end
def join_er(body)
 join('er', body)
end
def join_ian(body)
 join('ian', body)
end

%w(real social ruby).map(&method(:join_ist)) # => ["realist", "socialist", "rubyist"]
%w(sell climb haskell).map(&method(:join_er)) # => ["seller", "climber", "haskeller"]
%w(music physic Janis).map(&method(:join_ian)) # => ["musician", "physician", "Janisian"]

join = ->suffix,body{ body + suffix }.curry #Procオブジェクトをカリー化する
# カリー化されたProcオブジェクトに一部の引数を部分適用する。
# これにより残りの引数を受けるProcオブジェクトが生成される。
join['ist'] # => #<Proc:0x007fdf011ce1b0 (lambda)>
%w(real social ruby).map(&join['ist']) # => ["realist", "socialist", "rubyist"]
%w(sell climb haskell).map(&join['er']) # => ["seller", "climber", "haskeller"]
%w(music physic Janis).map(&join['ian']) # => ["musician", "physician", "Janisian"]

is_escape = ->chr{ chr.ord == 27 }
is_back = ->chr{ [127, 8].include?(chr.ord) }
chr = "\e"
case chr
when is_escape then puts :escape
when is_back then puts :back
else puts :unknown
end
# >> escape

1. ちなみにこのコードではselfを直接ブロック内に渡していませんがその理由がRubiniusのソースには書いてあります。 ↩

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