From 595a4a591b6f4f863d52e28046e2fc1c51dfcad5 Mon Sep 17 00:00:00 2001
From: David Heinemeier Hansson <david@loudthinking.com>
Date: Wed, 29 Dec 2004 21:19:37 +0000
Subject: Rearranging dependencies

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@279 5ecf4fe2-1ee6-0310-87b1-e25e094e27de
---
 activesupport/lib/binding_of_caller.rb | 81 ++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 activesupport/lib/binding_of_caller.rb

(limited to 'activesupport/lib/binding_of_caller.rb')

diff --git a/activesupport/lib/binding_of_caller.rb b/activesupport/lib/binding_of_caller.rb
new file mode 100644
index 0000000000..64b945158c
--- /dev/null
+++ b/activesupport/lib/binding_of_caller.rb
@@ -0,0 +1,81 @@
+begin
+  require 'simplecc'
+rescue LoadError
+  def Continuation.create(*args, &block)
+    cc = nil; result = callcc {|c| cc = c; block.call(cc) if block and args.empty?}
+    result ||= args
+    return *[cc, *result]
+  end
+end
+
+# This method returns the binding of the method that called your
+# method. It will raise an Exception when you're not inside a method.
+#
+# It's used like this:
+#   def inc_counter(amount = 1)
+#     Binding.of_caller do |binding|
+#       # Create a lambda that will increase the variable 'counter'
+#       # in the caller of this method when called.
+#       inc = eval("lambda { |arg| counter += arg }", binding)
+#       # We can refer to amount from inside this block safely.
+#       inc.call(amount)
+#     end
+#     # No other statements can go here. Put them inside the block.
+#   end
+#   counter = 0
+#   2.times { inc_counter }
+#   counter # => 2
+#
+# Binding.of_caller must be the last statement in the method.
+# This means that you will have to put everything you want to
+# do after the call to Binding.of_caller into the block of it.
+# This should be no problem however, because Ruby has closures.
+# If you don't do this an Exception will be raised. Because of
+# the way that Binding.of_caller is implemented it has to be
+# done this way.
+def Binding.of_caller(&block)
+  old_critical = Thread.critical
+  Thread.critical = true
+  count = 0
+  cc, result, error, extra_data = Continuation.create(nil, nil)
+  error.call if error
+
+  tracer = lambda do |*args|
+    type, context, extra_data = args[0], args[4], args
+    if type == "return"
+      count += 1
+      # First this method and then calling one will return --
+      # the trace event of the second event gets the context
+      # of the method which called the method that called this
+      # method.
+      if count == 2
+        # It would be nice if we could restore the trace_func
+        # that was set before we swapped in our own one, but
+        # this is impossible without overloading set_trace_func
+        # in current Ruby.
+        set_trace_func(nil)
+        cc.call(eval("binding", context), nil, extra_data)
+      end
+    elsif type == "line" then
+      nil
+    elsif type == "c-return" and extra_data[3] == :set_trace_func then
+      nil
+    else
+      set_trace_func(nil)
+      error_msg = "Binding.of_caller used in non-method context or " +
+        "trailing statements of method using it aren't in the block."
+      cc.call(nil, lambda { raise(ArgumentError, error_msg) }, nil)
+    end
+  end
+
+  unless result
+    set_trace_func(tracer)
+    return nil
+  else
+    Thread.critical = old_critical
+    case block.arity
+      when 1 then yield(result)
+      else yield(result, extra_data)        
+    end
+  end
+end
-- 
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