[ruby-core:94320] [Ruby master Feature#15815] Add option to raise NoMethodError for OpenStruct

[mtsmfm@gmail.com]

Issue #15815 has been updated by mtsmfm (Fumiaki Matsushima).


koi-san

Sorry for being late.
I've added https://bugs.ruby-lang.org/issues/15996?next_issue_id=15993&prev_issue_id=15998#note-17

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Feature #15815: Add option to raise NoMethodError for OpenStruct
https://bugs.ruby-lang.org/issues/15815#change-80707

* Author: mtsmfm (Fumiaki Matsushima)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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GitHub PR: https://github.com/ruby/ruby/pull/2164

Currently, `OpenStruct#method_missing` returns `nil` even if the key isn't registered.

```ruby
require 'ostruct'
os = OpenStruct.new({a: 1})
os.a #=> 1
os.b #=> nil
```

I'd like to add `exception` option to raise `NoMethodError` in such case.

```ruby
require 'ostruct'
os = OpenStruct.new({a: 1}, exception: true)
os.a #=> 1
os.b #=> NoMethodError
```

## Use case

I sometimes use OpenStruct as a JSON API response wrapper.
It's useful to use method call instead of key access (`obj[:key]`) because we can use `Symbol#to_proc` if it's a method (for example `users.map(&:id)`)

But I want to prevent typo for a key name. Currently `users.map(&:idd)` just returns `[nil,...]`

Even if we have this `exception` option, we can't enable this option for JSON parser easily though:

```ruby
JSON.parse(response, object_class: Class.new(OpenStruct) { def initialize(hash); super(hash, exception: true); end })
```

What do you think?

----

I've searched with "openstruct nomethoderror" on bugs.ruby-lang.org though, please let me know if it's duplicated.
https://bugs.ruby-lang.org/search?utf8=%E2%9C%93&scope=&q=nomethoderror+openstruct



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