From: "rosenfeld (Rodrigo Rosenfeld Rosas)" <rr.rosas@...>
Date: 2013-08-12T23:26:32+09:00
Subject: [ruby-core:56578] [CommonRuby - Feature #8643] Add Binding.from_hash


Issue #8643 has been updated by rosenfeld (Rodrigo Rosenfeld Rosas).


I didn't notice I replied only to Koichi Sasada when replying to the ruby-core list. Is it possible to set it up so that the reply-to field is set to ruby-core?

Here is some discussion from us from those e-mails so that everyone could have access to it:

> (2013/08/10 20:47), Rodrigo Rosenfeld Rosas wrote:
>> I'm not sure how else to explain it 
>>
>> The only API example I know that requires a binding is the ERB one 
>>
>> It's designed to be used this way:
>>
>> a = 1
>> b = 2
>> erb.result binding # both a and b are available inside the template as
>> well as other methods and variables, like erb
> Koichi wrote:
>
> Please try:
>
> require 'erb'
> bind = binding
> bind.local_variable_set(:a, 1)
> bind.local_variable_set(:b, 2)
> puts ERB.new("<%= a %> and <%= b %>").result(bind)
> #=> 1 and 2

That works, but it is too much trouble for a simple requirements and
besides that more methods and variables may leak when using the current
binding.

That's why people will often use the "OpenStruct.new(hash){binding}"
trick, since it's much shorter, but still a hack in my opinion.

This is often used in automation tools like Chef or Puppet where the
recipe settings (stored as a hash, usually) should be available for some
templates.

Suppose you have the NewRelic settings under settings[:new_relic] hash
(eg.: { application_name: 'My App', enable_rum: true })

In such cases, when generating the newrelic.yml from a newrelic.yml.erb
template, those tools would process it as:

File.write 'newrelic/location/newrelic.yml', ERB.new(File.read
'path/to/newrelic.yml.erb').result
OpenStruct.new(settings[:new_relic]){binding}

That's why I've created two tickets based on this common requirement. On
this specific one I'm suggesting a Binding.from_hash(hash) to make it
easier to get a binding from a hash for usage in such API's. The other
one suggested ERB to accept also a hash, instead of a binding for #result.

(there's more, I'll post as another comment)
----------------------------------------
Feature #8643: Add Binding.from_hash
https://bugs.ruby-lang.org/issues/8643#change-41113

Author: rosenfeld (Rodrigo Rosenfeld Rosas)
Status: Open
Priority: Normal
Assignee: ko1 (Koichi Sasada)
Category: 
Target version: 


Binding.from_hash would work like:

class Binding
  def self.from_hash(hash)
    OpenStruct.new(hash){ binding }
  end
end

It would simplify things like:

ERB.new(IO.read 'template.erb').result Binding.from_hash(template_local: 'example')

Or if you need to eval some code in another process (JRuby, for instance) and need to pass some arguments to the eval code in a hash form.

I didn't want to pollute Hash by adding Hash#to_binding. I believe Binding.from_hash is more appropriate.


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