class_eval(aString) vs class_eval(aBlock)

Ruby
1

Hi,

why does class_eval behave differently is you pass a string or a block
to it?
This simple test

| class A
| def test_str; p self.class.class_eval("@@v"); end
| def test_blk; p self.class.class_eval { @@v }; end
| end
|
| class B < A
| def initialize; @@v = “v.B”; end
| end
|
| B.new.test_str
| B.new.test_blk

gives this (unexpected?) result

| $ ruby ./cv2.rb
| “v.B”
| ./cv2.rb:3:in test_blk': uninitialized class variable @@v in A (NameError) | from ./cv2.rb:3:inclass_eval’
| from ./cv2.rb:3:in class_eval' | from ./cv2.rb:3:intest_blk’
| from ./cv2.rb:11

2

On 2006.01.24 21:19, Gioele B. wrote:

| class B < A
| ./cv2.rb:3:in test_blk': uninitialized class variable @@v in A (NameError) | from ./cv2.rb:3:in class_eval’
| from ./cv2.rb:3:in class_eval' | from ./cv2.rb:3:in test_blk’
| from ./cv2.rb:11

Reason for that is that all blocks are closures (they ‘enclose’ the
scope they were defined in). In this case, @@v is bound to the @@v
in class A at the time you create the block.

Gioele [email protected]

E