Feature #11925
closed
Struct construction with kwargs
Added by prijutme4ty (Ilya Vorontsov) over 9 years ago.
Updated over 7 years ago.
Description
Propose to make Struct subclass constructors which accept keyword arguments. Not sure, if it's reasonable to allow .new accept kwargs, so may be should use different method named like .create:
Point = Struct.new(:x,:y, :color)
pt_1 = Point.create(x: 1, y: 2) # => Point<x: 1, y: 2, color: nil>
pt_2 = Point.create!(x: 1, y: 2) # => ArgumentError, color not specified.
It will greatly simplify work with big structures, especially in cases when struct layout changes and for cases when structure can have lots of non-significant values. It also allows simpler ways to use implement default values for struct members.
We looked at this issue in yesterday's developer meeting. Nobody there was against the functionality -- but the name. create! doesn't sound appropriate at all. create also not that obvious for non-English speakers like us that it expects keywords.
What about new_from_kwargs(**kwargs) ? It's a bit long, but it describes the functionality exactly.
https://github.com/ruby/ruby/pull/1468
A proposal for an implementation.
irb(main):001:0> MyClass = Struct.new(:a, :b, :c)
=> MyClass
irb(main):002:0> MyClass.new_from_kwargs(a:1, c: 3)
=> #<struct MyClass a=1, b=nil, c=3>
irb(main):003:0> MyClass.new_from_kwargs(1, 2, 3, b: 3)
=> #<struct MyClass a=1, b=3, c=3>
irb(main):004:0> MyClass.new_from_kwargs(d: 4)
NameError: no member 'd' in struct
from (irb):4:in `new_from_kwargs'
from (irb):4
from ./irb:11:in `<main>'
irb(main):005:0> MyClass.new_from_kwargs(1, 2, 4, 5, b: 3)
IndexError: offset 3 too large for struct(size:3)
from (irb):5:in `new_from_kwargs'
from (irb):5
from ./irb:11:in `<main>'
irb(main):006:0>
Herwin W wrote:
irb(main):003:0> MyClass.new_from_kwargs(1, 2, 3, b: 3)
=> #<struct MyClass a=1, b=3, c=3>
Why does new_from_kwargs accept other than keyword arguments?
To be prepared for "the great unification of constructors" of course.
It looked like a pretty logical step to support while I was coding this. It's also pretty easy to remove again
- Has duplicate Feature #9209: Struct instances creatable with named args added
Another idea is introducing another method to define own struct, such as T = Struct.define(:a, :b); T.new(a: 1, b: 2) and so on.
(just idea) Moreover we can extend Struct with some properties, like: Struct.define(:a, b: :read_only).
These ideas are provided by another person.
- Has duplicate Feature #13272: Keyword argument to instantiate a subclass of Struct added
Similar to one commented by ko1, how about this interface?
T = Struct.new(:a, :b, keyword_argument: true)
T.new(a: 1, b: 2)
As keyword_argument is long, another option is:
Struct.new(:a, :b, keyword_args: true)
What if Struct.new([:a, :b]) created a class with the desired constructor?
I vote for the keyword argument (e.g. keyword_init:) to Struct#new.
Matz.
knu (Akinori MUSHA) wrote:
What if Struct.new([:a, :b]) created a class with the desired constructor?
If you'd compare the two possible constructors:
Struct.new(:a, :b)
Struct.new([:a, :b])
There is nothing in the second one that would indicate the second creates a keyword constructor. If I hadn't read this discussion, I would just expect them to behave the same.
- Status changed from Open to Closed
Applied in changeset trunk|r61137.
struct.c: add keyword_init option to Struct.new
to initialize struct with keyword arguments.
[Feature #11925] [close GH-1771]
As Matz approved, I committed only keyword_init option which is equivalent to "Point.create(x: 1, y: 2)" in original suggestion. If you still want "Point.create!" version which raises ArgumentError (keyword_init initializes unspecified fields with nil), please file another ticket.
- Related to Feature #15076: Struct to raise error when keyword arguments used but not enabled added
- Related to Feature #15222: Add a way to distinguish between Struct classes with and without keyword initializer added
- Related to Feature #16806: Struct#initialize accepts keyword arguments too by default added
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Added by k0kubun (Takashi Kokubun) over 7 years ago
struct.c: add keyword_init option to Struct.new
to initialize struct with keyword arguments.
[Feature #11925] [close GH-1771]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61137 b2dd03c8-39d4-4d8f-98ff-823fe69b080e