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module EventMachine
# Utility method for coercing arguments to an object that responds to :call.
# Accepts an object and a method name to send to, or a block, or an object
# that responds to :call.
#
# @example EventMachine.Callback used with a block. Returns that block.
#
# cb = EventMachine.Callback do |msg|
# puts(msg)
# end
# # returned object is a callable
# cb.call('hello world')
#
#
# @example EventMachine.Callback used with an object (to be more specific, class object) and a method name, returns an object that responds to #call
#
# cb = EventMachine.Callback(Object, :puts)
# # returned object is a callable that delegates to Kernel#puts (in this case Object.puts)
# cb.call('hello world')
#
#
# @example EventMachine.Callback used with an object that responds to #call. Returns the argument.
#
# cb = EventMachine.Callback(proc{ |msg| puts(msg) })
# # returned object is a callable
# cb.call('hello world')
#
#
# @overload Callback(object, method)
# Wraps `method` invocation on `object` into an object that responds to #call that proxies all the arguments to that method
# @param [Object] Object to invoke method on
# @param [Symbol] Method name
# @return [<#call>] An object that responds to #call that takes any number of arguments and invokes method on object with those arguments
#
# @overload Callback(object)
# Returns callable object as is, without any coercion
# @param [<#call>] An object that responds to #call
# @return [<#call>] Its argument
#
# @overload Callback(&block)
# Returns block passed to it without any coercion
# @return [<#call>] Block passed to this method
#
# @raise [ArgumentError] When argument doesn't respond to #call, method name is missing or when invoked without arguments and block isn't given
#
# @return [<#call>]
def self.Callback(object = nil, method = nil, &blk)
if object && method
lambda { |*args| object.__send__ method, *args }
else
if object.respond_to? :call
object
else
blk || raise(ArgumentError)
end # if
end # if
end # self.Callback
end # EventMachine
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