Should you assign it to a variable?

Let us suppose that you’re going to compute some value, and then send it to another function. Which snippet is better (using lhs as shorthand for a variable identifier and rhs() as shorthand for the right-hand side expression)?

lhs = rhs()
do_work(lhs)

do_work(rhs())

My short answer is it depends. Here is my informal set of heuristics:

• • Is a type-cast involved (e.g., in a statically typed language like C)? If so, assign it to a variable.
  • Would the variable name be a meaningful one that would provide non-obvious information about the nature of the computation? If so, assign it to a variable. For instance, if a long right-hand side expression computes perplexity, ppl = ... or perplex = ... is about as useful as an inline comment.
  • Is the computation used again in the same scope? If so, assign it to a variable.
  • Is the right-hand side just a very complicated expression? If so, consider assigning it to a variable, and try to give it an informative name.
  • Otherwise, do not assign it to a variable.