From: samuel@... Date: 2021-05-27T11:10:05+00:00 Subject: [ruby-core:104062] [Ruby master Feature#15567] Allow ensure to match specific situations Issue #15567 has been updated by ioquatix (Samuel Williams). I revisited this situation again. This behaviour is very confusing: ~~~ ruby def transaction begin puts "Begin Transaction" yield rescue puts "Abort Transaction" else puts "Commit Transaction" end end catch(:ball) do transaction do throw :ball end end ~~~ In particular, trying to handle this by using `ensure ... unless $!` can fail in some situations due to scope of $! ~~~ ruby def transaction begin puts "Begin Transaction" yield rescue puts "Abort Transaction" ensure puts "Commit Transaction" unless $! end end catch(:ball) do begin raise "Problem" rescue transaction do throw :ball end end end ~~~ It seems like we must involve some elaborate state tracking in order to get the correct behaviour (calling either abort or commit predictably). So, I believe we should reconsider this feature, or some evolution of it. ---------------------------------------- Feature #15567: Allow ensure to match specific situations https://bugs.ruby-lang.org/issues/15567#change-92236 * Author: ioquatix (Samuel Williams) * Status: Rejected * Priority: Normal * Assignee: ioquatix (Samuel Williams) ---------------------------------------- There are some situations where `rescue Exception` or `ensure` are not sufficient to correctly, efficiently and easily handle abnormal flow control. Take the following program for example: ``` def doot yield ensure # Did the function run to completion? return "abnormal" if $! end puts doot{throw :foo} puts doot{raise "Boom"} puts doot{"Hello World"} catch(:foo) do puts doot{throw :foo} end ``` Using `rescue Exception` is not sufficient as it is not invoked by `throw`. Using `ensure` is inefficient because it's triggered every time, even though exceptional case might never happen or happen very infrequently. I propose some way to limit the scope of the ensure block: ``` def doot yield ensure when raise, throw return "abnormal" end ``` The scope should be one (or more) of `raise`, `throw`, `return`, `next`, `break`, `redo`, `retry` (everything in `enum ruby_tag_type` except all except for `RUBY_TAG_FATAL`). Additionally, it might be nice to support the inverted pattern, i.e. ``` def doot yield ensure when not return return "abnormal" end ``` Inverted patterns allow user to specify the behaviour without having problems if future scopes are introduced. `return` in this case matches both explicit and implicit. -- https://bugs.ruby-lang.org/ Unsubscribe: