Unexpected behavior with App::Persistence and BW::JSON

[bensie]

It seems that BubbleWrap::JSON can't parse a string that comes from persisted storage:

> App::Persistence["foo"] = BubbleWrap::JSON.generate({"foo"=>nil,"bar"=>nil})
=> "{\"foo\":null,\"bar\":null}"

> BubbleWrap::JSON.parse App::Persistence["foo"]
2012-07-24 12:03:57.789 Amigo Booth[72204:11603] -[__NSCFString bytes]: unrecognized selector sent to instance 0x9d68c80
2012-07-24 12:03:57.874 Amigo Booth[72204:11603] json.rb:19:in `parse:': NSInvalidArgumentException: -[__NSCFString bytes]: unrecognized selector sent to instance 0x9d68c80 (RuntimeError)
=> #<RuntimeError: NSInvalidArgumentException: -[__NSCFString bytes]: unrecognized selector sent to instance 0x9d68c80>

[dmarkow]

This is a RubyMotion bug specifically, I just filed a ticket.

(main)> NSUserDefaults.standardUserDefaults["foo"] = "bar"
=> "bar"
(main)> NSUserDefaults.standardUserDefaults["foo"].class
=> String
(main)> other_string = "bar"
=> "bar"
(main)> other_string.class
=> String
(main)> NSUserDefaults.standardUserDefaults["foo"].class.ancestors
=> [String, NSMutableString, NSString, Comparable, NSObject, Kernel]
(main)> other_string.class.ancestors
=> [String, NSMutableString, NSString, Comparable, NSObject, Kernel]
(main)> other_string.methods - NSUserDefaults.standardUserDefaults["foo"].methods
=> [:"transform:", :each_codepoint, :codepoints, :each_byte, :bytes, :ascii_only?, :valid_encoding?, :"force_encoding:", :pointer, :to_data, :"setbyte:", :"getbyte:", :bytesize, :"camelize:", :camelize, :underscore, :to_color]
# WTF?

So while the string that RubyMotion returns for standardUserDefaults["foo"] is a String, it's missing a couple methods that a other RubyMotion Strings have (in this case, we specifically need to_data).

I'll look into a temporary workaround until this gets fixed upstream.

[dmarkow]

To clarify, this doesn't just affect the JSON parsing. For example, you can't use camelize on strings returned from standardUserDefaults either.

[bensie]

Thanks for taking the time to investigate and come up with a workaround!

[dmarkow]

Update from Laurent, looks like we'll need to keep the dup in there indefinitely.

Strings created in Ruby do respond to these additional methods because they are differently implemented: they use a binary storage to conform to the Ruby specs. Pure NSStrings do not have a binary storage (they are character-based) which is why to_data & friends are not there.

I agree it can be confusing at the first glance (especially since the same class is returned, again for spec conformance) but this is a historical heritage from MacRuby.

I believe that to_s or dup will return a "ruby" string if called on an NSString. You can use that before calling to_data to make sure it will always work