Re: Proposal: Add "level" argument to assert()

[Enrico Colombini <erix@...>]

On 09/04/2011 16.41, HyperHacker wrote:
> assert() is a convenient function for checking for error conditions in
> one statement. A common expression:
> if not foo then error("Invalid foo") end
> can be shortened to:
> assert(foo, "Invalid foo")

I like assert, but I rarely use it in Lua because of performance 
consideration when I need more information. Maybe I'm mistaken (I would 
gladly be) but I'm under the impression that:

  local f = assert(io.open(fname, 'r'), 'cannot open: ' .. fname)

always performs the string concatenation, regardless of success or 
failure, while the if..then equivalent:

  local f = io.open(fname, 'r')
  if not f then print('cannot open: ' .. fname) end

only concatenates in case of error. In some cases (e.g. function 
argument check) this could lead to a significant difference in execution 
time and memory usage.

Maybe a varargs (print-like) version of assert() could avoid this 
dilemma. Or a generic:

  assert(cond, func, ...)

that calls func(...) in case of assertion failure, before exiting.

--
  Enrico