From: kokumeiko@... Date: 2017-05-05T14:16:11+00:00 Subject: [ruby-core:81008] [Ruby trunk Bug#13543] local variable declaration Issue #13543 has been updated by eiko (eiko kokuma). true, the parser detects the local variable early on, but it does not ignore the method until the point of assignment: ~~~ ruby def foo @foo ||= "foo" end p local_variables #=> [:foo] p foo.size #=> 3 foo = foo.size #=> NoMethodError ~~~ so, despite the fact that local variables are determined before run-time, there's a mechanic in place to make sure they don't shadow methods until they are assigned. but why shadow the method mid-assignment when that's not common language design or seemingly useful as a design choice? sorry if i'm in the wrong place for this. i had wanted to discuss this with ruby experts before raising the issue as a potential bug, but outside of stackoverflow, i don't know how best to communicate with people who know ruby well. ---------------------------------------- Bug #13543: local variable declaration https://bugs.ruby-lang.org/issues/13543#change-64667 * Author: eiko (eiko kokuma) * Status: Open * Priority: Normal * Assignee: * Target version: * ruby -v: 2.4.0rc1 * Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN ---------------------------------------- The following code snippet generates a strange error: ~~~ ruby def foo @foo ||= "foo" end foo = foo.size #=> undefined method 'size' for nil:NilClass (NoMethodError) ~~~ I expect the code to create a local variable `foo` which is assigned the value `3`. I expect this because in assignment, the right size of `=` is always resolved before being bound to the left side of `=`. In my mind, `foo` should refer to the `foo()` method right up to the point that a value is assigned to the local variable which shadows it. It is confusing and unexpected to have a period of limbo in which `foo()` is overshadowed by an unassigned local variable mid-declaration. In other languages, declaration and initial assignments are atomic, so this code would throw errors: In python: ~~~ python foo = foo # NameError: name 'foo' is not defined ~~~ In rust: ~~~ c let foo = foo // error: cannot find value 'foo' in this scope. ~~~ But in ruby, a variable can be instantly declared and assigned to itself: ~~~ ruby foo = foo #=> nil ~~~ This goes against the common motifs of programming in ruby and other languages and can lead to the confusing error mentioned above. Is there a reason local variables should be declared prior to resolving the assignment expression in ruby? I could find no documented reason for this design choice, leading me to believe it is a bug. -- https://bugs.ruby-lang.org/ Unsubscribe: