I get the following different results:
Test 1:
def myblock
x = 1
y = 1
yield(x)
[x, y]
end
myblock do |x|
y = 10
end
# => [1,1]
Test 2:
x = 1
y = 1
1.upto(2) do |x|
y = 20
end
[x,y]
# => [1,20]
Variables created outside the block are available in the block. Why are they so?
That is how the scope of a local variable is defined. A local variable can percolate into a block, but not into a method definition.
def myblock
x = 1
y = 1
z = yield(x)
puts "y=#{y}, z=#{z}"
[x, y]
end
myblock do |x|
y = 10
end
y=1, z=10
#=> [1, 1]
This shows that three things are going on here:
y in the block is unrelated to the y in myblock. That's because the scope of the y in the block is confined to the block. Ruby can only get her hands on what is returned by the block, not on what's going on inside of it.y in the block, but only because y = 10 was the last statement executed in the block. The execution of that statement returns 10, so 10 is returned by the block. Had the block contained y = 10; 7, 7 would have been returned.yield(x) is not captured by the variable y in myblock, so it has no effect.1.1 It's a little-known fact that Ruby actually shoots such values into outer space.
y is defined before the block that y in the block is the same y. If you remove y = 1 and you run the code (try it) youy is initialized before the block that it is the same y inside the block. Remove y = 1 and [x,y] will raise an exception: "Name error: undefined local variable 'y'". It has to be that way for the block to be able to use previously-defined variables in the block calculations. Here y = 1.upto(2) { |x| 20 } would work (but it doesn't make much sense).After more testing and searching:
For Test1, x and y is method level local variable and they don't share the scope with block. y in the block is a new local variable(block level).
For Test2, x and y is class level local variable and they share the scope with block, y in the block is still the outside y(class level).
It's all because I messed up the scope, thanks all.