Re: Against enforce()

[Steven Schveighoffer]

On Fri, 18 Mar 2011 04:14:12 -0400, Kagamin <s...@here.lot> wrote:
Walter Bright Wrote:

1. Asserts and contracts are for detecting program BUGS. They are not  
for
validating user input, checking for disk full, file not found errors,  
etc.

2. Enforce is for validating user input, checking for disk full, file  
not found
errors, etc. Enforce is NOT for use in contracts or checking for  
program bugs.


Any use of enforce in Phobos that is checking for program bugs is  
itself a bug
and should be entered into bugzilla for fixing.

So this is a bug? This is a contract, not a validation of user input.

struct Iota(N, S) if ((isIntegral!N || isPointer!N) && isIntegral!S)
 {
    private N current, pastLast;
    private S step;
    this(N current, N pastLast, S step)
    {
        enforce((current <= pastLast && step > 0) ||
                (current >= pastLast && step < 0));
        this.current = current;
        this.step = step;

This is a good example of why it's difficult to decide what "user input"  
is.  One could consider that the 'user' in this case is the developer  
using the library, but I don't think that's the right choice.

I'd say it's a bug, this is clearly a contract, since the data being  
passed into the ctor can easily not be user input (i.e. it's most likely  
two literals that will never depend on a user).  If it is user input, the  
caller of the ctor should enforce the user input before passing it to iota.

-Steve