From: chris@... Date: 2021-02-10T10:12:54+00:00 Subject: [ruby-core:102444] [Ruby master Bug#17619] if false foo=42; end creates a foo local variable set to nil Issue #17619 has been updated by chrisseaton (Chris Seaton). > but why would a variable be created in a program-flow primitive ie (if etc) if that condition is such that that code is never executed? Local variables are 'created' (we could say 'declared') during parse-time in Ruby. That's why they become defined as soon as they are found lexically. We could also call this 'hoisting'. ---------------------------------------- Bug #17619: if false foo=42; end creates a foo local variable set to nil https://bugs.ruby-lang.org/issues/17619#change-90327 * Author: pkmuldoon (Phil Muldoon) * Status: Open * Priority: Normal * Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN ---------------------------------------- Take this following code ``` [1] pry(main)> defined?(foo) nil [2] pry(main)> if false [2] pry(main)* foo = 42 [2] pry(main)* end [3] pry(main)> defined?(foo) "local-variable" ``` The inner scope inherits the parent scope (ok) but also modifies the parent scope even if the child scope is never entered. A lesser effect of this: ``` [1] pry(main)> defined?(bar) nil [2] pry(main)> if false [2] pry(main)* bar = 99 [2] pry(main)* end [3] pry(main)> defined?(bar) "local-variable" [5] pry(main)> bar 99 ``` That somewhat lesser affecting because I can just about accept a variable invading the parent scope, and existing after, as a hoisting event. But surely that should not be the case in the negative program-flow case? The side effects of this are defined?(foo) can't be trusted anymore. Apologies if this bug has been filed. I did search for it, but couldn't find anything quite matching it. Thanks! -- https://bugs.ruby-lang.org/ Unsubscribe: