Re: Disabling assert function

["Stuart P. Bentley" <stuart@...>]

Here's how I'd write an assert that saves both compilation and execution  
for last, and also avoids concatenations:

function compiled_assert(cond, --the condition to assert on
formatfs, --the code for a function to calculate the message if the assert  
fails
...) --the values that the function will need to compute its message

  if cond then --if the assert does not fail
    return cond, formatfs, ... --return all arguments (like assert())
  else error( --raise an error
    string.format( --with the formatting arguments
      --returned from the execution of the function coded in the passed  
string
      --with the passed parameters
      assert(loadstring(formatfs))(...)
    ))
  end
end

So Marc's original example would be written as

compiled_assert( object:isValid(),
[[ ... = object
return "object %s is not valid", object:getName()]],
object)

In this way, all the call to assert sends, in addition to the initial  
condition calculation, are the initial values required to derive the final  
message, with no additional computation expended unless required.

Of course, this would really only be called for in situations where  
calculating the message for the assert is prohibitively expensive. In most  
cases, this complexity is not called for, and would just be premature  
optimization (trading a disproportionate amount of memory for CPU).

On Thu, 20 May 2010 09:53:26 -0700, Luiz Henrique de Figueiredo  
<lhf@tecgraf.puc-rio.br> wrote:

> > function assertc(condn,fun)
> >     if not condn then assert(false,fn()) end
> > end
>
> Here's an assert on esteroids that can be used to avoid concatenations
> for instance: