From: manga.osyo@...
Date: 2019-08-13T10:15:07+00:00
Subject: [ruby-core:94321] [Ruby master Feature#15815] Add option to raise NoMethodError for OpenStruct

Issue #15815 has been updated by osyo (manga osyo).


What about adding block arguments to `OpenStruct.new` like `Hash` instead of options?

```ruby
h = Hash.new {|hash, key|
  raise(IndexError, "hash[#{key}] has no value")
}

# Error: in `block in <main>': hash[1] has no value (IndexError)
h[1]


require "ostruct"

# Adding block arguments like Hash
os = OpenStruct.new({a: 1}) {|open_struct, method_name|
  raise(NoMethdError, "undefined method `#{method_name}' for #{open_struct}")
}

# Error: in `block in <main>': undefined method `b' for #<OpenStruct a=1> (NoMethodError)
os.b
```


----------------------------------------
Feature #15815: Add option to raise NoMethodError for OpenStruct
https://bugs.ruby-lang.org/issues/15815#change-80708

* Author: mtsmfm (Fumiaki Matsushima)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
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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