Assuming I have the following proc:
a = Proc.new do
puts "start"
yield
puts "end"
end
Also assuming I pass a
to another method which subsequently calls instance_eval
on another class with that block, how can I now pass a block onto the end of that method which gets yielded in a
.
For example:
def do_something(a,&b)
AnotherClass.instance_eval(&a) # how can I pass b to a here?
end
a = Proc.new do
puts "start"
yield
puts "end"
end
do_something(a) do
puts "this block is b!"
end
Output should of course should be:
start
this block is b!
end
How can I pass the secondary block to a in the instance_eval
?
I need something like this for the basis of a Ruby templating system I'm working on.
You can't use yield in a
. Rather, you have to pass a Proc
object. This would be the new code:
def do_something(a,&b)
AnotherClass.instance_exec(b, &a)
end
a = Proc.new do |b|
puts "start"
b.call
puts "end"
end
do_something(a) do
puts "this block is b!"
end
yield
is only for methods. In this new code, I used instance_exec
(new in Ruby 1.9) which allows you to pass parameters to the block. Because of that, we can pass the Proc object b
as a parameter to a
, which can call it with Proc#call()
.