在Ruby中对字符串和block求解

class ProcFactory
def create
Proc.new {}
end
end

proc = ProcFactory.new.create
eval "self.class", proc.binding    #=> ProcFactory

Select[:column1, :column2].from[:table1, :table2].where do
equal table1.id, table2.table1_id
end

Delete.from[:table1].where do
exists(Select[:column2].from[:table2].where do
equal table1.column1, table2.column2
end
end

def where(&block)
@text += " where "
tables.concat(eval("respond_to?(:tables) ? tables : []", block.binding)).inspect
instance_eval &block
end

eval "respond_to?(:tables) ? tables : []", block.binding

Delete.from[:table1].where do .. end 

tables.concat([:table1]) 

delete from table1 where exists (select column2 from table2 where table1.column1 = table2.column2) 

class Delete
def self.from
Delete.new
end
def [](*args)
@text = "delete from "
@text += args.join ","
@tables = args
self
end
attr_reader :tables
def where(&block)
@text += " where "
instance_eval &block
end
def exists(statement)
@text += "exists "
@text += statement
end
end
class Select
def self.[](*args)
self.new(*args)
end
def initialize(*columns)
@text = "select "
@text += columns.join ","
end
def from
@text += " from "
self
end
def [](*args)
@text += args.join ","
@tables = args
self
end
def tables
@tables
end
def where(&block)
@text += " where "
tables.concat(eval("respond_to?(:tables) ? tables : []", block.binding)).inspect
instance_eval &block
end
def method_missing(sym, *args)
super unless @tables.include? sym
klass = Class.new
klass.class_eval do
def initialize(table)
@table = table
end
def method_missing(sym, *args)
@table.to_s + "." + sym.to_s
end
end
klass.new(sym)
end
def equal(*args)
@text += args.join "="
end
end