Bug #19416
closedInconsistent behaviour for Struct.new without any member_names
Description
When I simply declare a Struct without any arguments, I get an error:
irb(main):001:0> Struct.new
(irb):1:in `new': wrong number of arguments (given 0, expected 1+) (ArgumentError)
from (irb):1:in `<main>'
But Struct has an option to pass a class name as the first argument, which will create the struct as a constant in the Struct namespace. If this argument is given, there is no ArgumentError
irb(main):002:0> Struct.new('Foo')
=> Struct::Foo
This results in a rather pointless class
irb(main):003:0> Struct::Foo.new(1)
(irb):3:in `initialize': struct size differs (ArgumentError)
from (irb):3:in `new'
irb(main):004:0> Struct::Foo.new
=> #<struct Struct::Foo>
This behaviour is not documented in the Struct class, but I would guess this is not how it is intended to be.
Updated by jeremyevans0 (Jeremy Evans) almost 2 years ago
I submitted a pull request to fix this: https://github.com/ruby/ruby/pull/7290. Not ready for merge yet as the debug gem's tests needs to be fixed not to use such a struct.
Updated by zverok (Victor Shepelev) almost 2 years ago
FWIW, Data
consciously allows member-less definitions, intended to be a tag/case values:
class Request
Success = Data.new(:body)
NotFound = Data.new
The latter is rendered consistently with Success
, convenient to reuse in pattern-matching, and can be expanded later when the architecture needs this.
It might be that the same logic applies to memberless Struct
to some extent (even if its intended usage is different from Data
, consistency in such things between the two might be desirable).
Updated by matz (Yukihiro Matsumoto) almost 2 years ago
After consideration, I think we should allow empty Struct
even without the name for consistency.
Matz.
Updated by mame (Yusuke Endoh) almost 2 years ago
Just for record. What made matz change his mind was the following code I wrote.
Cons = Struct.new(:car, :cdr)
Nil = Struct.new()
All we need to change Ruby is a simple code that shows a use case.
Updated by jeremyevans0 (Jeremy Evans) almost 2 years ago
matz (Yukihiro Matsumoto) wrote in #note-3:
After consideration, I think we should allow empty
Struct
even without the name for consistency.
I submitted a pull request to implement this: https://github.com/ruby/ruby/pull/7587
Updated by jeremyevans (Jeremy Evans) over 1 year ago
- Status changed from Open to Closed
Applied in changeset git|f8e7048348d022814736d0a7e49f2f2494db6a2f.
Allow anonymous memberless Struct
Previously, named memberless Structs were allowed, but anonymous
memberless Structs were not.
Fixes [Bug #19416]