Problem with Pickaxe and Yaml

ruby-talk
1

I've got the Pickaxe book (2nd edition) and was doing some of the Yaml
code on page 417. I cannot seem to get the expected results.

Example:

require 'yaml'

class Special

    def initialize(valuable, volatile, precious)
        @valuable = valuable
        @volatile = volatile
        @precious = precious
    end

    def to_yaml_properties
        %w{@precious @valuable}
    end

    def to_s
        "#@valuable #@volatile #@precious"
    end
end

obj = Special.new("Hello", "there", "world")
data = YAML.dump(obj)
obj = YAML.load(data)

puts obj["valuable"]

The last line throws an error, shouldn't it print out the value for
"valuable"?

I also tried this for the last line:

puts data["valuable"]

Thanks for any help on this.

···

--
Posted via http://www.ruby-forum.com/.

2

Mark Haliday wrote:

I've got the Pickaxe book (2nd edition) and was doing some of the Yaml code on page 417. I cannot seem to get the expected results.

Example:

require 'yaml'

class Special

    def initialize(valuable, volatile, precious)
        @valuable = valuable
        @volatile = volatile
        @precious = precious
    end

    def to_yaml_properties
        %w{@precious @valuable}
    end

    def to_s
        "#@valuable #@volatile #@precious"
    end
end

obj = Special.new("Hello", "there", "world")
data = YAML.dump(obj)
obj = YAML.load(data)

puts obj["valuable"]

The last line throws an error, shouldn't it print out the value for "valuable"?

No. There's no "" method defined. Try 'puts obj'.

That line isn't in the example, btw.

Regards,

Dan

3

no... obj becomes an instance of class Special, and acts just like the
object before you dumped it.

greg@oracle ~ $ irb
irb(main):001:0> class Foo
irb(main):002:1> def bar
irb(main):003:2> puts "hello"
irb(main):004:2> end
irb(main):005:1> end
=> nil
irb(main):006:0> a = Foo.new
=> #<Foo:0xb7d76310>
irb(main):008:0> require "yaml"
=> true
irb(main):009:0> data = YAML.dump(a)
=> "!ruby/object:Foo {}\n\n"
irb(main):010:0> b = YAML.load(data)
=> #<Foo:0xb7c253f4>
irb(main):011:0> b.bar
hello
=> nil

···

On 11/21/05, Mark Haliday <markhaliday@yahoo.com> wrote:

I've got the Pickaxe book (2nd edition) and was doing some of the Yaml
code on page 417. I cannot seem to get the expected results.

Example:

require 'yaml'

class Special

    def initialize(valuable, volatile, precious)
        @valuable = valuable
        @volatile = volatile
        @precious = precious
    end

    def to_yaml_properties
        %w{@precious @valuable}
    end

    def to_s
        "#@valuable #@volatile #@precious"
    end
end

obj = Special.new("Hello", "there", "world")
data = YAML.dump(obj)
obj = YAML.load(data)

puts obj["valuable"]

The last line throws an error, shouldn't it print out the value for
"valuable"?

4

I've got the Pickaxe book (2nd edition) and was doing some of the Yaml
code on page 417. I cannot seem to get the expected results.

Example:

require 'yaml'

class Special

    def initialize(valuable, volatile, precious)
        @valuable = valuable
        @volatile = volatile
        @precious = precious
    end

attr_reader :valuable

    def to_yaml_properties
        %w{@precious @valuable}
    end

    def to_s
        "#@valuable #@volatile #@precious"
    end
end

obj = Special.new("Hello", "there", "world")
data = YAML.dump(obj)
obj = YAML.load(data)

puts obj["valuable"]

puts obj.valuable

Hope that helps.

James Edward Gray II

···

On Nov 21, 2005, at 1:21 PM, Mark Haliday wrote:

5

I've got the Pickaxe book (2nd edition) and was doing some of the Yaml
code on page 417. I cannot seem to get the expected results.

In this case: try walking through your code with irb.

obj = Special.new("Hello", "there", "world")
data = YAML.dump(obj)
obj = YAML.load(data)

puts obj["valuable"]

puts obj.valuable

puts data["valuable"]

data is "just a string" ...

s.

···

On Tue, 22 Nov 2005 04:21:05 +0900, Mark Haliday wrote:

6

Uh ... your code is *NOT* precisely the example. There's nothing in the
original example that does a ["valuable"] call to either the original or the
reloaded objects.

puts "Before: #{ obj }"
data = Marshal.dump( obj )
obj = Marshal.load( data )
puts "After: #{ obj }"

Which uses the #to_s function to get access to the internal variables.

If you do the same, you should see the output that they show on p417.

If you aren't going to quote the source verbatim, you probably should expect
the exact same output.

Anyways, hope that helps.

j.

···

On 11/21/05, Mark Haliday <markhaliday@yahoo.com> wrote:

I've got the Pickaxe book (2nd edition) and was doing some of the Yaml
code on page 417. I cannot seem to get the expected results.

Example:

require 'yaml'

class Special

def initialize(valuable, volatile, precious)
@valuable = valuable
@volatile = volatile
@precious = precious
end

def to_yaml_properties
%w{@precious @valuable}
end

def to_s
"#@valuable #@volatile #@precious"
end
end

obj = Special.new("Hello", "there", "world")
data = YAML.dump(obj)
obj = YAML.load(data)

puts obj["valuable"]

The last line throws an error, shouldn't it print out the value for
"valuable"?

I also tried this for the last line:

puts data["valuable"]

Thanks for any help on this.

--
Posted via http://www.ruby-forum.com/\.

--
"Remember. Understand. Believe. Yield! -> http://ruby-lang.org"

Jeff Wood

7

Actually it's working as expected.
obj does not have a method. However you could do the following:

class Special
   attr_reader :valuable
end

puts obj.valuable

or

YAML is serializing obj then deserializing it.
The catch is in the first line of data.

'puts data' shows
- --- !ruby/object:Special
precious: world
valuable: hello

That first line tells YAML that it's going to be loading the data into an instance of 'Special' If you were to remove that top line then load it

data = "precious: world\nvaluable: hello"
obj = YAML.load data

it would act as a hash and behave like you wanted it to behave.

puts obj['valuable']
hello

···

On Nov 21, 2005, at 11:21 AM, Mark Haliday wrote:

I've got the Pickaxe book (2nd edition) and was doing some of the Yaml
code on page 417. I cannot seem to get the expected results.

Example:

require 'yaml'

class Special

    def initialize(valuable, volatile, precious)
        @valuable = valuable
        @volatile = volatile
        @precious = precious
    end

    def to_yaml_properties
        %w{@precious @valuable}
    end

    def to_s
        "#@valuable #@volatile #@precious"
    end
end

obj = Special.new("Hello", "there", "world")
data = YAML.dump(obj)
obj = YAML.load(data)

puts obj["valuable"]

The last line throws an error, shouldn't it print out the value for
"valuable"?

I also tried this for the last line:

puts data["valuable"]

Thanks for any help on this.

--
Posted via http://www.ruby-forum.com/\.

8

Daniel.Berger wrote:

No. There's no "" method defined. Try 'puts obj'.

That line isn't in the example, btw.

Regards,

Dan

But a similar example is used on page 758 (near the bottom of the page).

If I just do a:

puts obj

It puts out both values, when I just want to get the one in "valuable".

Thanks.

···

--
Posted via http://www.ruby-forum.com/\.

9

Oops, ignore that junk and pay attention to the others who actually read the problem. :wink:

James Edward Gray II

···

On Nov 21, 2005, at 1:36 PM, James Edward Gray II wrote:

On Nov 21, 2005, at 1:21 PM, Mark Haliday wrote:

I've got the Pickaxe book (2nd edition) and was doing some of the Yaml
code on page 417. I cannot seem to get the expected results.

Example:

require 'yaml'

class Special

    def initialize(valuable, volatile, precious)
        @valuable = valuable
        @volatile = volatile
        @precious = precious
    end

attr_reader :valuable

    def to_yaml_properties
        %w{@precious @valuable}
    end

    def to_s
        "#@valuable #@volatile #@precious"
    end
end

obj = Special.new("Hello", "there", "world")
data = YAML.dump(obj)
obj = YAML.load(data)

puts obj["valuable"]

puts obj.valuable

10

Mark Haliday wrote:

Daniel.Berger wrote:

No. There's no "" method defined. Try 'puts obj'.

That line isn't in the example, btw.

Regards,

Dan
   
But a similar example is used on page 758 (near the bottom of the page).

If I just do a:

puts obj

It puts out both values, when I just want to get the one in "valuable".

Thanks.

When you write "puts obj" you are calling puts with the object 'obj' as a parameter. The prints the result of obj.to_s to stdout.

The to_s method for an object typically returns a string. You can see that in the example the to_s method is defined as returning a string containing the values of three instance variables.

Perhaps part of the confusion has to do with the to_yaml_properties method. The to_yaml_properties method is only a clue indicating which data you would like included in the yaml-ization of an object and not what you can expect from dumping the object.

The difference between the example on the bottom of page 758 and your example is that the object loaded in the pickaxe example is a Hash and so it responds to the method.

I hope that I've helped more than confused.

Matthew