[ruby-core:113743] [Ruby master Feature#19708] Support `attr_reader :foo?`
Issue #19708 has been reported by AMomchilov (Alexander Momchilov). ---------------------------------------- Feature #19708: Support `attr_reader :foo?` https://bugs.ruby-lang.org/issues/19708 * Author: AMomchilov (Alexander Momchilov) * Status: Open * Priority: Normal ---------------------------------------- Creating reader methods with `attr_reader` is preferable over defining them by hand, not only because it's more convenient, but also because it hits a fast path in MRI (see `VM_METHOD_TYPE_IVAR`). Since local and instance variables can't end with `?`, you can't use `attr_reader` to define predicate-style methods for boolean values, like: ```ruby class Person attr_reader(:name, :age, :active?) # invalid attribute name `active?' (NameError) def initialize @name = "Bob" @age = 30 @active = true end end ``` It would be nice if `attr_reader` (and friends) could behave like: ```ruby def active? = @active ``` (`attr_writer` and `attr_accessor` couldn't do the same, since `def active?=(new_value)` isn't valid, so they'd probably stick with `def active=(new_value)`) -- https://bugs.ruby-lang.org/
Issue #19708 has been updated by AMomchilov (Alexander Momchilov). You can workaround this by using `attr_reader` to create the optimized method, `alias_method` to give it the nice `active?` name, and then `remove_method` to delete the original non-`?` name: ```ruby module PredicateHelper # Or just monkey-patch Module, I won't sue :D def define_predicate(predicate_name) ivar_name = predicate_name.to_s.delete_suffix("?") attr_reader(ivar_name) alias_method(predicate_name, ivar_name) remove_method(ivar_name) end end ``` Usage: ```ruby class Person extend PredicateHelper attr_reader :name, :age define_predicate :active? def initialize @name = "Bob" @age = 30 @active = true end end bob = Person.new p [bob.name, bob.age, bob.active?] # ["Bob", 30, true] # Shows that `#active?` is just aliasing the now-deleted `#active` p Person.instance_method(active?) # => #<UnboundMethod: Person#active?(active)() Untitled 2.rb:6> ``` ---------------------------------------- Feature #19708: Support `attr_reader :foo?` https://bugs.ruby-lang.org/issues/19708#change-103391 * Author: AMomchilov (Alexander Momchilov) * Status: Open * Priority: Normal ---------------------------------------- Creating reader methods with `attr_reader` is preferable over defining them by hand, not only because it's more convenient, but also because it hits a fast path in MRI (see `VM_METHOD_TYPE_IVAR`). Since local and instance variables can't end with `?`, you can't use `attr_reader` to define predicate-style methods for boolean values, like: ```ruby class Person attr_reader(:name, :age, :active?) # invalid attribute name `active?' (NameError) def initialize @name = "Bob" @age = 30 @active = true end end ``` It would be nice if `attr_reader` (and friends) could behave like: ```ruby def active? = @active ``` (`attr_writer` and `attr_accessor` couldn't do the same, since `def active?=(new_value)` isn't valid, so they'd probably stick with `def active=(new_value)`) -- https://bugs.ruby-lang.org/
Issue #19708 has been updated by rubyFeedback (robert heiler). Personally I agree with the proposal, largely because I love methods that end with a trailing '?' - I think that was a good language decision choice matz made to indicate query-like methods via ?. Such as: if game_over? notify_the_user_that_the_game_is_over end I kind of have stopped using attr* methods though, in part because I could not use them for trailing '?', but in part also because I seem to become lazier whenever I use attr methods. Additionally some methods need to do some clean-up and sanitization steps in certain classes, and the attr-methods only really are super-simple, not allowing for extra actions here - e. g. just to be used as setters and getters. I do seem to remember that there was a reason given as to why no trailing '?' method exists for the attr-family of methods. I think matz mentioned this once on the bugtracker, but I forgot the explanation.
You can workaround this by using attr_reader to create the optimized method, alias_method to give it the nice active? name, and then remove_method to delete the original non-? name:
There are many work arounds. I simply use the "def" variant. :P def age? @age end; alias age age? (Although for larger classes, I shifted towards using a Hash that keeps track of all instance variables instead. I found that once you have like ~20 different instance variables, a Hash seems easier to understand than individual instance variables.) Note that I think your proposal has not been clear in regards to what attr_reader would do. Are these two separate methods or not? Consider this: attr_reader :foobar attr_reader :foobar? Both would query over @foobar, right? But are these the same methods or different? e. g. when someone undefines/removes them, is the other one removed or not? That should also be clarified in the proposal IMO, just to make it instantly clear to the dev team what is meant exactly. ---------------------------------------- Feature #19708: Support `attr_reader :foo?` https://bugs.ruby-lang.org/issues/19708#change-103396 * Author: AMomchilov (Alexander Momchilov) * Status: Open * Priority: Normal ---------------------------------------- Creating reader methods with `attr_reader` is preferable over defining them by hand, not only because it's more convenient, but also because it hits a fast path in MRI (see `VM_METHOD_TYPE_IVAR`). Since local and instance variables can't end with `?`, you can't use `attr_reader` to define predicate-style methods for boolean values, like: ```ruby class Person attr_reader :name, :age, :active? # invalid attribute name `active?' (NameError) def initialize @name = "Bob" @age = 30 @active = true end end ``` It would be nice if `attr_reader` (and friends) could behave like: ```ruby def active? = @active ``` (`attr_writer` and `attr_accessor` couldn't do the same, since `def active?=(new_value)` isn't valid, so they'd probably stick with `def active=(new_value)`) -- https://bugs.ruby-lang.org/
Issue #19708 has been updated by AMomchilov (Alexander Momchilov).
You can workaround this by using attr_reader to create the optimized method, alias_method to give it the nice active? name, and then remove_method to delete the original non-? name:
There are many workarounds. I simply use the "def" variant. :P
def age? @age end; alias age age?
That's not equivalent. It's the "next best thing", but it creates a `VM_METHOD_TYPE_IVSEQ` method, not a more optimized `VM_METHOD_TYPE_IVAR`.
Are these two separate methods or not? Consider this:
attr_reader :foobar attr_reader :foobar?
Both would query over @foobar, right?
Yep.
But are these the same methods or different? e. g. when someone undefines/removes them, is the other one removed or not?
There's no ambiguity here, they're two different methods, that just happen to share an underlying instance variable, no different than if you had written them by hand. You can undef one, or the other, or both. ---------------------------------------- Feature #19708: Support `attr_reader :foo?` https://bugs.ruby-lang.org/issues/19708#change-103408 * Author: AMomchilov (Alexander Momchilov) * Status: Open * Priority: Normal ---------------------------------------- Creating reader methods with `attr_reader` is preferable over defining them by hand, not only because it's more convenient, but also because it hits a fast path in MRI (see `VM_METHOD_TYPE_IVAR`). Since local and instance variables can't end with `?`, you can't use `attr_reader` to define predicate-style methods for boolean values, like: ```ruby class Person attr_reader :name, :age, :active? # invalid attribute name `active?' (NameError) def initialize @name = "Bob" @age = 30 @active = true end end ``` It would be nice if `attr_reader` (and friends) could behave like: ```ruby def active? = @active ``` (`attr_writer` and `attr_accessor` couldn't do the same, since `def active?=(new_value)` isn't valid, so they'd probably stick with `def active=(new_value)`) -- https://bugs.ruby-lang.org/
Issue #19708 has been updated by byroot (Jean Boussier). This was proposed and rejected by Matz several time in the past (see the linked issues). Not saying it's impossible to try again, but you'll likely need a much stronger case than that to convince Matz. ---------------------------------------- Feature #19708: Support `attr_reader :foo?` https://bugs.ruby-lang.org/issues/19708#change-103415 * Author: AMomchilov (Alexander Momchilov) * Status: Open * Priority: Normal ---------------------------------------- Creating reader methods with `attr_reader` is preferable over defining them by hand, not only because it's more convenient, but also because it hits a fast path in MRI (see `VM_METHOD_TYPE_IVAR`). Since local and instance variables can't end with `?`, you can't use `attr_reader` to define predicate-style methods for boolean values, like: ```ruby class Person attr_reader :name, :age, :active? # invalid attribute name `active?' (NameError) def initialize @name = "Bob" @age = 30 @active = true end end ``` It would be nice if `attr_reader` (and friends) could behave like: ```ruby def active? = @active ``` (`attr_writer` and `attr_accessor` couldn't do the same, since `def active?=(new_value)` isn't valid, so they'd probably stick with `def active=(new_value)`) -- https://bugs.ruby-lang.org/
Issue #19708 has been updated by Eregon (Benoit Daloze). Agreed this would be nice and make such query methods more optimized. In https://bugs.ruby-lang.org/issues/12046#note-3 it sounds to me matz was looking for a concrete use case, I think there are plenty in the wild. I think a PR/patch for this would help to make progress (it might not be trivial). ---------------------------------------- Feature #19708: Support `attr_reader :foo?` https://bugs.ruby-lang.org/issues/19708#change-103416 * Author: AMomchilov (Alexander Momchilov) * Status: Open * Priority: Normal ---------------------------------------- Creating reader methods with `attr_reader` is preferable over defining them by hand, not only because it's more convenient, but also because it hits a fast path in MRI (see `VM_METHOD_TYPE_IVAR`). Since local and instance variables can't end with `?`, you can't use `attr_reader` to define predicate-style methods for boolean values, like: ```ruby class Person attr_reader :name, :age, :active? # invalid attribute name `active?' (NameError) def initialize @name = "Bob" @age = 30 @active = true end end ``` It would be nice if `attr_reader` (and friends) could behave like: ```ruby def active? = @active ``` (`attr_writer` and `attr_accessor` couldn't do the same, since `def active?=(new_value)` isn't valid, so they'd probably stick with `def active=(new_value)`) -- https://bugs.ruby-lang.org/
Issue #19708 has been updated by AMomchilov (Alexander Momchilov). Hey Jean & Benoit, thanks for finding those prior discussions. I tried searching for them before posting, but the question mark makes it really hard to find anything relevant, haha I think the use case is clear: defining reader methods that are both fast (`VM_METHOD_TYPE_IVAR`) _and_ idiomatic (`#foo?` over `#is_foo`). Today you're forced to choose one or the other: * Either you get idomatic naming with `def foo? = @foo`, but a slower `VM_METHOD_TYPE_ISEQ` method, * Or you get a faster method with `attr_reader :is_foo`, but lose the idomatic naming. With the proposed change, you can get the best of both worlds. There's also the case for convenience: you no longer have to split your attribute readers into two groups: ```ruby class C attr_reader :a, :c, :d, :f # Group 1: non-predicate methods can use attr_reader def initialize # ... end # ... other stuff # Group 2: predicate methods need explicit `def`s def b? = @b def e? = @e end ```
I think a PR/patch for this would help to make progress (it might not be trivial).
I took a cursory look: I think it'll definitely be a challenge, but I think it's something to take on. Ideally, I'd like to first get some sort of tentative interest, to make sure I don't put effort into a PR that's dead-on-arrival :D ---------------------------------------- Feature #19708: Support `attr_reader :foo?` https://bugs.ruby-lang.org/issues/19708#change-103649 * Author: AMomchilov (Alexander Momchilov) * Status: Open * Priority: Normal ---------------------------------------- Creating reader methods with `attr_reader` is preferable over defining them by hand, not only because it's more convenient, but also because it hits a fast path in MRI (see `VM_METHOD_TYPE_IVAR`). Since local and instance variables can't end with `?`, you can't use `attr_reader` to define predicate-style methods for boolean values, like: ```ruby class Person attr_reader :name, :age, :active? # invalid attribute name `active?' (NameError) def initialize @name = "Bob" @age = 30 @active = true end end ``` It would be nice if `attr_reader` (and friends) could behave like: ```ruby def active? = @active ``` (`attr_writer` and `attr_accessor` couldn't do the same, since `def active?=(new_value)` isn't valid, so they'd probably stick with `def active=(new_value)`) -- https://bugs.ruby-lang.org/
participants (4)
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AMomchilov (Alexander Momchilov) -
byroot (Jean Boussier)
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Eregon (Benoit Daloze)
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rubyFeedback (robert heiler)