Problem using OpenStruct with ERB

问题:

EDIT: forgot to include my environment info... Win7x64, RubyInstaller Ruby v1.9.1-p378

EDIT 2: just updated to v1.9.1, patch 429, and still getting this same error.

Edit 3: running this same code in Ruby v1.8.7, patch 249, works fine. so it's v1.9.1 that broke it, apparently.

I'm new to using ERB and the samples i could find are... ummm... less than helpful... having played around with ERB for about an hour, I got some basic examples working (finally), but I have no idea why this doesn't work...

require 'ostruct'
require 'erb'

data = {:bar => "bar"}
vars = OpenStruct.new(data)

template = "foo "
erb = ERB.new(template)

vars_binding = vars.send(:binding)
puts erb.result(vars_binding)

this code produces the following error:

irb(main):007:0> puts erb.result(vars_binding)
NameError: undefined local variable or method `bar' for main:Object
        from (erb):1
        from C:/Ruby/v1.9.1/lib/ruby/1.9.1/erb.rb:753:in `eval'
        from C:/Ruby/v1.9.1/lib/ruby/1.9.1/erb.rb:753:in `result'
        from (irb):7
        from C:/Ruby/v1.9.1/bin/irb:12:in `'

why is it looking at the main:Object binding? I told it to use the binding from the OpenStruct by passing in vars_binding

can someone fill me in on why it doesn't work, and help me get it to work?

回答1:

Fix to Problem:

I stumbled upon this question when encountering the same type of error with similar code in Ruby 1.9.2.

I'm new to Ruby so I can't explain what is happening. I continued to search online and found this blog post that has an approach that seems to work. After modifying your example to incorporate this approach I end up with the following, working, code:

require 'ostruct'
require 'erb'

class ErbBinding < OpenStruct
    def get_binding
        return binding()
    end
end

data = {:bar => "baz"}
vars = ErbBinding.new(data)

template = "foo <%= bar %>"
erb = ERB.new(template)

vars_binding = vars.send(:get_binding)
puts erb.result(vars_binding)

---

Additional Information:

_{When the code is run thru the IRB, I get:}

require 'ostruct'
=> true
require 'erb'
=> true

class ErbBinding < OpenStruct
    def get_binding
        return binding()
    end
end
=> nil

data = {:bar => "baz"}
=> {:bar=>"baz"}
vars = ErbBinding.new(data)
=> #<ErbBinding bar="baz">

template = "foo <%= bar %>"
=> "foo <%= bar %>"
erb = ERB.new(template)
=> #<ERB:0x2b73370 @safe_level=nil, @src="#coding:IBM437\n_erbout = ''; _erbout.concat \"foo \"; _erbout.concat(( bar ).to_s); _erbout.force_encoding(__ENCODING__)", @enc=#<Encoding:IBM437>, @filename=nil>

vars_binding = vars.send(:get_binding)
=> #<Binding:0x2b6d418>
puts erb.result(vars_binding)
foo baz
=> nil

回答2:

The problem is where the binding is being executed. The 1.8.7-way obj.send(:binding) does not work anymore (see issue2161), the environment must be the object itself. So use instance_eval:

require 'ostruct'
require 'erb'

namespace = OpenStruct.new(:first => 'Salvador', :last => 'Espriu')
template = 'Name: <%= first %> <%= last %>'
ERB.new(template).result(namespace.instance_eval { binding })
#=> Name: Salvador Espriu

More about this issue in this answer.

回答3:

What's your environment look like? This code worked for me (I just changed the string "bar" to "baz" to disambiguate in my brain, and added it to the template):

require 'ostruct'
require 'erb'

data = {:bar => "baz"}
vars = OpenStruct.new(data)

template = "foo <%= bar %>"
erb = ERB.new(template)

vars_binding = vars.send(:binding)
puts erb.result(vars_binding)

When I run it, I get:

defeateds-MacBook-Pro:Desktop defeated$ ruby erb.rb 
foo baz

Under 1.8.7 on OSX:

defeateds-MacBook-Pro:Desktop defeated$ ruby -v
ruby 1.8.7 (2009-06-08 patchlevel 173) [universal-darwin10.0]

回答4:

Looks like this does not work with higher ruby versions

with ruby 2.1.1

[19] pry(main)> name = "samtoddler"
=> "Suresh"
[20] pry(main)> template_string = "My name is <%= name %>"
=> "My name is <%= name %>"
[21] pry(main)> template = ERB.new template_string
=> #<ERB:0x007fadf3491c38
 @enc=#<Encoding:UTF-8>,
 @filename=nil,
 @safe_level=nil,
 @src="#coding:UTF-8\n_erbout = ''; _erbout.concat \"My name is \"; _erbout.concat(( name ).to_s); _erbout.force_encoding(__ENCODING__)">
[22] pry(main)> puts template.result
NameError: undefined local variable or method `name' for main:Object
from (erb):1:in `<main>'

with ruby 1.9.3

[2] pry(main)> name = "samtoddler"
=> "Suresh"
[3] pry(main)> template_string = "My name is <%= name %>"
=> "My name is <%= name %>"
[4] pry(main)> template = ERB.new template_string
=> #<ERB:0x007f9be2a1fdf8
 @enc=#<Encoding:UTF-8>,
 @filename=nil,
 @safe_level=nil,
 @src=
  "#coding:UTF-8\n_erbout = ''; _erbout.concat \"My name is \"; _erbout.concat(( name ).to_s); _erbout.force_encoding(__ENCODING__)">
[5] pry(main)> puts template.result
My name is samtoddler

So it gives error but still works in 1.9.3 and all the versions below 1.9.3.