From: "Cédric Finance" <pticedric@...>
Date: 2007-04-20T18:27:25+09:00
Subject: Re: what does this code do ? from libxml schema-test.rb ???

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I think that the block is called only if there is an error or a warning
during the validation.
Otherwise the block is not called. In case of an error/warning, the block
get the message
and whether it is an error or a warning. It is possible that the block is
called for each warnings
and errors. I will check the extension.

On 4/20/07, Reuben Grinberg <reuben.grinberg@aya.yale.edu> wrote:
>
> aktxyz@gmail.com wrote:
> > At the bottom of the schema-test.rb in the libxml gem, there is this
> > bit of code.
> >
> > This is when I realize I still have a long way to go with Ruby.  I
> > don't get the {} block right after the 1st line, how does this work,
> > its like a {} block in do-end block ? weird.
> >
> > Of course, what I am after is the message in the case schema
> > validation fails !
> >
> >
> > if doc.validate_schema(schema) { |message, error| puts "#{error ?
> > 'error' : 'warning'} : #{message}" }
> >   puts "validation passed"
> > else
> >   puts "validation failed"
> > end
> >
>
> I'm not sure exactly which set of {}'s you are referring to, so I'll
> explain all of them.
>
> In ruby, functions can take as an argument another function to call.
>
> (More detailed information here
>
> http://eli.thegreenplace.net/2006/04/18/understanding-ruby-blocks-procs-and-methods
>
> but I'll summarize)
>
> Here is an example of a function that takes another function as an
> argument, and then calls that function:
>
> irb>def print_it
> #yield is a special keyword that calls the passed function
>         puts yield
> end
>
> irb> print_it { "bob" }
> bob
>
> Furthermore, the function passed in can take an argument:
>
> irb>def print_it2
>         puts yield(3)
> end
>
> irb> print_it { |x| x + 1 }
> 4
>
>
> So in your code,
> if doc.validate_schema(schema) { |message, error|
>
> message is the message from validating and error is the error...
>
> So if you wanted to make a function that returned the message:
> def validate(doc, schema)
>         doc.validate_schema(schema) { |message, error| return message }
> end
>
> Or, if you want to get the error and message:
>
> the_message, the_error = nil
> if doc.validate_schema(schema) { |message, error|
>         the_message, the_error = message, error
>         puts "#{error ? error' : 'warning'} : #{message}"
> }
>     puts "validation passed"
>   else
>     puts "validation failed"
>   end
>
>
> Are you asking about #{message}?
>
> This is the way to get the value of a variable inside a string:
>
> irb>a = 5
> irb>puts a
> 5
> irb>puts "a"
> a
> irb>puts "#{a}"
> 5
>
> irb> greeting = "hello"
> irb> puts "#{greeting}, Bob!"
> hello Bob!
>
> Hope that helps,
> Reuben
>
>

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