Issue #20093 has been updated by kjtsanaktsidis (KJ Tsanaktsidis). Would `class extension` just be syntax sugar for this: ``` String.class_eval do def exclude?(string) = !include?(string) end ``` or would it behave differently in some way? ---------------------------------------- Feature #20093: Syntax or keyword to reopen existing classs/modules, never to define new classs/modules https://bugs.ruby-lang.org/issues/20093#change-105876 * Author: tagomoris (Satoshi Tagomori) * Status: Open * Priority: Normal ---------------------------------------- `class A` and `module B` will reopen existing class A or module B to add/re-define methods if A/B exists. Otherwise, these will define the new class/module A/B. But, in my opinion, the code of `class A` for patching existing classes doesn't work expectedly when `A` is not defined beforehand. It expects other codes to define `A` before being called. For example: ```ruby # string_exclude.rb class String def exclude?(string) !include?(string) end end ``` This code expects that there is the `String` class, and it has the `include?` method. This code doesn't work if the file is loaded in the way below: ```ruby load('string_exclude.rb', true) ``` This code doesn't raise errors and will define an almost empty class (only with a method `exclude?` to raise NameError). It should be unexpected for every user. So, I want to propose a new syntax to reopen the existing class/module or raise errors if the specified class/module is not defined. ```ruby class extension String def exclude?(string) !include?(string) end end # adds #exclude? to String class class extension Stroooong def exclude?(string) !include?(string) end end # will raise NameError (or something else) ``` Some additional things: * `class extension String` (and `module extension String`) causes a compile error (SyntaxError) on Ruby 3.3. So we have space to add a keyword between class/module and the class/module name. * I don't have a strong opinion about the keyword name `extension`. An alternative idea is `reopen`. -- https://bugs.ruby-lang.org/

Issue #20093 has been updated by rubyFeedback (robert heiler). Dan0042 wrote: I am not entirely certain tagomoris meant to use **.class_eval** here. See his alternative suggestion of "reopen". Of course I may be wrong, but if I understood it correctly his issue request may be more related towards being able to extend something in ruby no matter if it is a class or a module or already-defined versus yet-to-be-defined; a bit like a "promise" of functionality, not unlike refinements make isolated modifications to existing classes/code. E. g.: class extension String class reopen String reopen String # just as an example to drop the class/module name altogether and may be shorter In particular in the last case, I have had use cases to want to **avoid** having to type either "class" or "module" altogether. I also agree with the use case of refinements, by the way, but I always felt the syntax awkward. This is also one slight problem I have here, in that I think "class foobar String" is too verbose - and it may also be a bit confusing for ruby users. But I think tagomoris has a point as well - the intention should be for a ruby developer to "modify behaviour xyz". As stated, I may be mistaken, so perhaps tagomoris can refer to the .class_eval example. We should ideally come up with a useful syntax, though - being an elegant language is one of ruby's strong points, even if what is elegant differs between individuals naturally. ---------------------------------------- Feature #20093: Syntax or keyword to reopen existing classs/modules, never to define new classs/modules https://bugs.ruby-lang.org/issues/20093#change-105878 * Author: tagomoris (Satoshi Tagomori) * Status: Open * Priority: Normal ---------------------------------------- `class A` and `module B` will reopen existing class A or module B to add/re-define methods if A/B exists. Otherwise, these will define the new class/module A/B. But, in my opinion, the code of `class A` for patching existing classes doesn't work expectedly when `A` is not defined beforehand. It expects other codes to define `A` before being called. For example: ```ruby # string_exclude.rb class String def exclude?(string) !include?(string) end end ``` This code expects that there is the `String` class, and it has the `include?` method. This code doesn't work if the file is loaded in the way below: ```ruby load('string_exclude.rb', true) ``` This code doesn't raise errors and will define an almost empty class (only with a method `exclude?` to raise NameError). It should be unexpected for every user. So, I want to propose a new syntax to reopen the existing class/module or raise errors if the specified class/module is not defined. ```ruby class extension String def exclude?(string) !include?(string) end end # adds #exclude? to String class class extension Stroooong def exclude?(string) !include?(string) end end # will raise NameError (or something else) ``` Some additional things: * `class extension String` (and `module extension String`) causes a compile error (SyntaxError) on Ruby 3.3. So we have space to add a keyword between class/module and the class/module name. * I don't have a strong opinion about the keyword name `extension`. An alternative idea is `reopen`. -- https://bugs.ruby-lang.org/

Issue #20093 has been updated by Edwing123 (Edwin Garcia). If this feature has the purpose of making class/module extension explicit (meaning you can clearly see that a class/module is being open again to be extended), then I agree with it. By the way, I think the keyword `open` is more suitable: ```ruby class Foo end # Yay! Explicitly opening # a class for extension. open class Foo def bar() end end ``` I like that we're being explicit, so with this when reading code, we can answer that the class/module is being open for extension and that its "canonical" definition is somewhere else. Regarding backward compatibility: - Should the `open` keyword be optional in order for existing code to keep working? If that's the case, then existing code that doesn't use `open` won't benefit from this: So, only code using `open` will opt into checking if the class/module being open is already defined. I believe this is fine, and this proposal opens the door to adding a feature that will make reading Ruby code more clearly. Eventually gems and applications can adopt the new keyword! ---------------------------------------- Feature #20093: Syntax or keyword to reopen existing classs/modules, never to define new classs/modules https://bugs.ruby-lang.org/issues/20093#change-105885 * Author: tagomoris (Satoshi Tagomori) * Status: Open * Priority: Normal ---------------------------------------- `class A` and `module B` will reopen existing class A or module B to add/re-define methods if A/B exists. Otherwise, these will define the new class/module A/B. But, in my opinion, the code of `class A` for patching existing classes doesn't work expectedly when `A` is not defined beforehand. It expects other codes to define `A` before being called. For example: ```ruby # string_exclude.rb class String def exclude?(string) !include?(string) end end ``` This code expects that there is the `String` class, and it has the `include?` method. This code doesn't work if the file is loaded in the way below: ```ruby load('string_exclude.rb', true) ``` This code doesn't raise errors and will define an almost empty class (only with a method `exclude?` to raise NameError). It should be unexpected for every user. So, I want to propose a new syntax to reopen the existing class/module or raise errors if the specified class/module is not defined. ```ruby class extension String def exclude?(string) !include?(string) end end # adds #exclude? to String class class extension Stroooong def exclude?(string) !include?(string) end end # will raise NameError (or something else) ``` Some additional things: * `class extension String` (and `module extension String`) causes a compile error (SyntaxError) on Ruby 3.3. So we have space to add a keyword between class/module and the class/module name. * I don't have a strong opinion about the keyword name `extension`. An alternative idea is `reopen`. -- https://bugs.ruby-lang.org/

Issue #20093 has been updated by Eregon (Benoit Daloze). tagomoris (Satoshi Tagomori) wrote in #note-4: Why not? For clarity, I mean `class_eval` with a block so there are no syntax highlighting hurdles and no extra runtime parsing. It is the existing way to be explicit this is reopening an existing class, and it fails clearly if the class was not defined before. The only downside I see is that doesn't make it easy to define and access constants defined under that class/module. A possibility in that case is to use `class_eval(String)`. I guess the motivation for this proposal is #19744? ---------------------------------------- Feature #20093: Syntax or keyword to reopen existing classs/modules, never to define new classs/modules https://bugs.ruby-lang.org/issues/20093#change-105887 * Author: tagomoris (Satoshi Tagomori) * Status: Open * Priority: Normal ---------------------------------------- `class A` and `module B` will reopen existing class A or module B to add/re-define methods if A/B exists. Otherwise, these will define the new class/module A/B. But, in my opinion, the code of `class A` for patching existing classes doesn't work expectedly when `A` is not defined beforehand. It expects other codes to define `A` before being called. For example: ```ruby # string_exclude.rb class String def exclude?(string) !include?(string) end end ``` This code expects that there is the `String` class, and it has the `include?` method. This code doesn't work if the file is loaded in the way below: ```ruby load('string_exclude.rb', true) ``` This code doesn't raise errors and will define an almost empty class (only with a method `exclude?` to raise NameError). It should be unexpected for every user. So, I want to propose a new syntax to reopen the existing class/module or raise errors if the specified class/module is not defined. ```ruby class extension String def exclude?(string) !include?(string) end end # adds #exclude? to String class class extension Stroooong def exclude?(string) !include?(string) end end # will raise NameError (or something else) ``` Some additional things: * `class extension String` (and `module extension String`) causes a compile error (SyntaxError) on Ruby 3.3. So we have space to add a keyword between class/module and the class/module name. * I don't have a strong opinion about the keyword name `extension`. An alternative idea is `reopen`. -- https://bugs.ruby-lang.org/

Issue #20093 has been updated by tagomoris (Satoshi Tagomori). I commented that "class_eval / module_eval can do the same things functionally.". However, as @Eregon pointed out, there is a different rule about constants around `class_eval` / `module_eval`. The method definition in `class_eval`/`module_eval` cannot refer to the class/module constants, and the block of `class_eval`/`module_eval` block cannot add/update the class/module constants. So, guiding people to use `class_eval` / `module_eval` instead of `class`/`module` for monkey patching should cause trouble and confusion. For the same reason, @matheusrich 's idea (`Module#reopen` method) is not ideal in my opinion. Adding methods instead of a new keyword should be much easier, but it's not what I want. The idea of top-level keywords, @Edwing123 's `open class` and @zverok 's `refine` look very hard to implement properly to me. `open class` conflicts with the existing `Kernel#open`. If `refine` is a method to take a block argument, it has the same problem with `class_eval`. If `refine` is a new top-level keyword (without following `do`), it will conflict with the `Module#refine` (Ruby core team members may be able to find any solution to avoid the conflict, though). So, My idea is still to have a new keyword between `class`/`module` and the name of class/module: `class extension String`. @Eregon It's true that this ticket's idea came up in an offline discussion about namespaces, but I thought this idea has its own value to be proposed as an independent feature, and I think it's (partially, at least) true because some people are making comments to agree with the intention. ---------------------------------------- Feature #20093: Syntax or keyword to reopen existing classs/modules, never to define new classs/modules https://bugs.ruby-lang.org/issues/20093#change-105936 * Author: tagomoris (Satoshi Tagomori) * Status: Open * Priority: Normal ---------------------------------------- `class A` and `module B` will reopen existing class A or module B to add/re-define methods if A/B exists. Otherwise, these will define the new class/module A/B. But, in my opinion, the code of `class A` for patching existing classes doesn't work expectedly when `A` is not defined beforehand. It expects other codes to define `A` before being called. For example: ```ruby # string_exclude.rb class String def exclude?(string) !include?(string) end end ``` This code expects that there is the `String` class, and it has the `include?` method. This code doesn't work if the file is loaded in the way below: ```ruby load('string_exclude.rb', true) ``` This code doesn't raise errors and will define an almost empty class (only with a method `exclude?` to raise NameError). It should be unexpected for every user. So, I want to propose a new syntax to reopen the existing class/module or raise errors if the specified class/module is not defined. ```ruby class extension String def exclude?(string) !include?(string) end end # adds #exclude? to String class class extension Stroooong def exclude?(string) !include?(string) end end # will raise NameError (or something else) ``` Some additional things: * `class extension String` (and `module extension String`) causes a compile error (SyntaxError) on Ruby 3.3. So we have space to add a keyword between class/module and the class/module name. * I don't have a strong opinion about the keyword name `extension`. An alternative idea is `reopen`. -- https://bugs.ruby-lang.org/