Re: Variable validation

Kent Dahl wrote:

> Chris Morris wrote:
>> 
>> I've got a class that has a number of instance variables, some of which
>> must be set prior to calling a save function to write these off somewhere
>> else. I'm doing the following:
>> 
>>       def check_required
>>         if @password == nil or @password.empty?
>>           or @firstName == nil or @firstName.empty?
>>           or @lastName == nil or @lastName.empty?
>>           or @nickName == nil or @nickName.empty?
>>           or @email == nil or @email.empty?
>>           raise RequiredDataMissingError('')
>>       end
>> 
>> .. but this smells.
> 
> If all these are accessible from the outside in reader methods, you
> could use an array of symbols and send:
> 
> <CODE>
> class RequiredDataMissingError < Exception
> end
> 
> class X
>   MANDATORY_FIELDS = [ :password, :firstName, :lastName,
>     :nickName, :email ]
>   
>   attr_accessor *MANDATORY_FIELDS
> 
>   def check_required
>     if MANDATORY_FIELDS.find{|field|
> value = self.send(field)
> value == nil or value.empty?
>       } then
>       raise RequiredDataMissingError
>     end
>   end
> end
> </CODE>
> 
> This does add a methodcall indirection, which could hurt you
> performancewise, but you seem to be (rightfully) trying to optimize for
> eyeball time :-)
> 

Or perhaps:

class C
  REQD = ['password', 'firstname', 'lastname']  #etc.

  def check_required
    missing = REQD.map {|r| (eval "@#{r}").to_s == '' ? nil : r}.compact
    missing.empty? or raise "How 'bout these, punk?  #{missing.join ', '}"
  end
end

Or if you hate using eval, you can check instance_variables to see if your 
field exists.  
To check if it's '' though, you'd need eval, or store a mapping from the 
variable name to 
the value somewhere, or use an accessor method, or ... (?)

Another tip:  If you're using constant strings as hash keys, I think it's 
better style 
and more efficient to use symbols instead:  {:a => 1, :b => 2, :c => 3} instead 
of {'a' 
=> 1, 'b' => 2, 'c' => 3}.  If you need the string value, you can use 
Symbol#id2name 
(aliased to Symbol#to_s) to convert it.