Derek Elkins wrote:
On Wed, 2008-01-30 at 22:19 -0500, Anton van Straaten wrote: ...
We discover a function called, say, "cos", probably by guessing it's name, run a very small number of simple tests on it, see the answers we expect, and decide that it's the function we want. Does anyone want to defend that on safety/correctness grounds? But some of us do it anyway.
It depends on the extent. Deciding between degrees and radians, this works perfectly if you have any idea what you are doing.
But deciding between degrees and radians is only one of the assumptions you'd be making, if you don't check the docs. In general, this argument sounds similar to the sort of arguments that are given in defense of all sorts of unsafe activities -- dynamic typechecking comes to mind, or unhygienic macros: "works perfectly if you have any idea what you are doing". While it may usually be true, it's often not considered a valid argument if safety and correctness are important.
Arguably, this -is- more defensible on a safety/correctness grounds than reading the documentation. Documentation can be out of date or wrong or right but the implementation is wrong. So it comes down to a matter of trust/convincing.
Reading the documentation alone isn't enough from a correctness perspective - you also need to test. As Reagan liked to put it, trust but verify. But similarly, testing alone isn't enough. There could be caveats in the documentation that could affect your program, that you don't detect in your tests. And yes, you also might come across a discrepancy between documentation and the actual behavior, which is something you'd want to investigate if correctness is important. Actual instances of discrepancies between documentation and code are a bug, but the fact that the two can get out of sync is a feature: it acts as a cross-check, and the purpose of cross-checks is that sometimes they fail. If you're concerned about safety and correctness, then ignoring available information about functions you use, and assuming that behavior is as you expect, still seems hard to defend, to me.