John Merlino wrote in post #998394:
> Hey all,
>
> This line of code I am having trouble understanding what it's doing:
>
> validates_presence_of :email, :unless => proc { |this|
> this.validation_context == :create_user }
>
> Basically, there is a code block that floats adjacent to a method. The
> method is called and returns a value. That yielded value is passed as an
> argument (local variable "this") into the code block and the code block
> returns a value to the method (in this case true or false since double
> equal is used and converts result into primitive (actually not but an
> object of type boolean) type boolean). But then I did a search for this
> method proc and its definition doesn't exist in application. However, a
> google search shows there is an object called proc. Since code blocks
> are not objects, instead just holding a context of logic sitting
> adjacent to a method which invokes them via yield, using proc is a way
> to convert a code block to an object. Hence, they can be stored in
> variables and called through the variables as a callable object. But as
> you see in the above example, proc is not instantiated like so:
> Proc.new. And even if you look at context, there will be no reason to
> use an instance of proc here, since we aren't storing anything into a
> variable for later use as a callable method, such as in this example:
>
> hello_world = Proc.new { |str| return str + 'world' }
>
> def fnc(new_fnc, *args)
> return unless new_fnc.respond_to?("call")
> new_fnc.call(*args)
> end
>
> puts fnc hello_world, 'hey'
>
> So my question is am I missing something here? What exactly is "proc"
> doing since it isn't an instance of Proc nor is it a method (there's no
> definition for it as I mentioned)?
>
> Thanks for response
Well I have been burned for making too detailed answers, so here is the
short version.
"validates_presence_of" is a method call, ":unless" is the key part of
the hash part of the parameters to "validates_presence_of", and the proc
(equivalent to Proc.new) part is sent as the value to key ":unless".
Hope that was short enough.
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