From: Reuben Grinberg <reuben.grinberg@...>
Date: 2007-04-20T14:40:06+09:00
Subject: Re: what does this code do ? from libxml schema-test.rb ???

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