[ruby-core:113954] [Ruby master Misc#19740] Block taking methods can't differentiate between a non-local return and a throw
Issue #19740 has been reported by byroot (Jean Boussier). ---------------------------------------- Misc #19740: Block taking methods can't differentiate between a non-local return and a throw https://bugs.ruby-lang.org/issues/19740 * Author: byroot (Jean Boussier) * Status: Open * Priority: Normal ---------------------------------------- Opening this as Misc, as at this stage I don't have a fully formed feature request. Ref: https://github.com/ruby/ruby/commit/1a3bcf103c582b20e9ea70dfed0ee68b24243f55 Ref: https://github.com/ruby/timeout/pull/30 Ref: https://github.com/rails/rails/pull/29333 ### Context Rails has this problem in the Active Record transaction API. The way it works is that it yields to a block, and if no error was raised the SQL transaction is committed, otherwise it's rolled back: ```ruby User.transaction do do_thing end # COMMIT ``` or ```ruby User.transaction do raise SomeError end # ROLLBACK ``` The problem is that there are more ways a method can be exited: ```ruby User.transaction do return # non-local exit end ``` ```ruby User.transaction do throw :something end ``` In the case of a non-local return, we'd want to commit the transaction, but in the case of a throw, particularly since it's internally used by `Timeout.timeout` since Ruby 2.1, we'd rather consider that an error and rollback. But as far as I'm aware, there is not way to distinguish the two cases. ```ruby def transaction returned = false yield returned = true ensure if $! # error was raised elsif returned # no uniwnd else # non-local return or throw, don't know end end ``` I think it could be useful to have a way to access the currently thrown object, similar to `$!` for such cases, or some other way to tell what is going on. There is some discussion going on in https://github.com/ruby/timeout/pull/30 about whether `Timeout` should throw or raise, and that may solve part of the problem, but regardless of where this leads, I think being able to check if something is being thrown would be valuable. cc @matthewd FYI @jeremyevans0 @Eregon -- https://bugs.ruby-lang.org/
Issue #19740 has been updated by Eregon (Benoit Daloze). I'm not sure it's good to be able to differentiate, because then it could be a mess if different gems consider return/throw/break differently, e.g. if Rails wants to commit on `return` but some other library only wants to commit on "natural return", or some difference in how they treat `throw`, etc. Personally if I would design such a transaction API I would only commit on natural return, I think people shouldn't "escape" the block via return/break/throw if they want to commit it. But I can also see the other side of the argument as discussed in https://github.com/ruby/timeout/pull/30, with the expected vs exceptional control flow. ---------------------------------------- Misc #19740: Block taking methods can't differentiate between a non-local return and a throw https://bugs.ruby-lang.org/issues/19740#change-103667 * Author: byroot (Jean Boussier) * Status: Open * Priority: Normal ---------------------------------------- Opening this as Misc, as at this stage I don't have a fully formed feature request. Ref: https://github.com/ruby/ruby/commit/1a3bcf103c582b20e9ea70dfed0ee68b24243f55 Ref: https://github.com/ruby/timeout/pull/30 Ref: https://github.com/rails/rails/pull/29333 ### Context Rails has this problem in the Active Record transaction API. The way it works is that it yields to a block, and if no error was raised the SQL transaction is committed, otherwise it's rolled back: ```ruby User.transaction do do_thing end # COMMIT ``` or ```ruby User.transaction do raise SomeError end # ROLLBACK ``` The problem is that there are more ways a method can be exited: ```ruby User.transaction do return # non-local exit end ``` ```ruby User.transaction do throw :something end ``` In the case of a non-local return, we'd want to commit the transaction, but in the case of a throw, particularly since it's internally used by `Timeout.timeout` since Ruby 2.1, we'd rather consider that an error and rollback. But as far as I'm aware, there is not way to distinguish the two cases. ```ruby def transaction returned = false yield returned = true ensure if $! # error was raised elsif returned # no uniwnd else # non-local return or throw, don't know end end ``` I think it could be useful to have a way to access the currently thrown object, similar to `$!` for such cases, or some other way to tell what is going on. There is some discussion going on in https://github.com/ruby/timeout/pull/30 about whether `Timeout` should throw or raise, and that may solve part of the problem, but regardless of where this leads, I think being able to check if something is being thrown would be valuable. cc @matthewd FYI @jeremyevans0 @Eregon -- https://bugs.ruby-lang.org/
Issue #19740 has been updated by matz (Yukihiro Matsumoto). Status changed from Open to Closed Unlike other languages e.g., C++ or Java, Ruby's `throw` is for non-local **return**, so that there's no reason to treat `return` and `throw` differently. Use exceptions to represent failures. I understand this issue was caused by `timeout` misused `catch/trhow`. But `timeout` is fixed now. Matz. ---------------------------------------- Misc #19740: Block taking methods can't differentiate between a non-local return and a throw https://bugs.ruby-lang.org/issues/19740#change-104266 * Author: byroot (Jean Boussier) * Status: Closed * Priority: Normal ---------------------------------------- Opening this as Misc, as at this stage I don't have a fully formed feature request. Ref: https://github.com/ruby/ruby/commit/1a3bcf103c582b20e9ea70dfed0ee68b24243f55 Ref: https://github.com/ruby/timeout/pull/30 Ref: https://github.com/rails/rails/pull/29333 ### Context Rails has this problem in the Active Record transaction API. The way it works is that it yields to a block, and if no error was raised the SQL transaction is committed, otherwise it's rolled back: ```ruby User.transaction do do_thing end # COMMIT ``` or ```ruby User.transaction do raise SomeError end # ROLLBACK ``` The problem is that there are more ways a method can be exited: ```ruby User.transaction do return # non-local exit end ``` ```ruby User.transaction do throw :something end ``` In the case of a non-local return, we'd want to commit the transaction, but in the case of a throw, particularly since it's internally used by `Timeout.timeout` since Ruby 2.1, we'd rather consider that an error and rollback. But as far as I'm aware, there is not way to distinguish the two cases. ```ruby def transaction returned = false yield returned = true ensure if $! # error was raised elsif returned # no uniwnd else # non-local return or throw, don't know end end ``` I think it could be useful to have a way to access the currently thrown object, similar to `$!` for such cases, or some other way to tell what is going on. There is some discussion going on in https://github.com/ruby/timeout/pull/30 about whether `Timeout` should throw or raise, and that may solve part of the problem, but regardless of where this leads, I think being able to check if something is being thrown would be valuable. cc @matthewd FYI @jeremyevans0 @Eregon -- https://bugs.ruby-lang.org/
participants (3)
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byroot (Jean Boussier) -
Eregon (Benoit Daloze)
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matz (Yukihiro Matsumoto)