[Swift-user] Resuming jobs when script has changed

[Mihael Hategan]

On Mon, 2014-05-19 at 21:47 +0000, Bronevetsky, Greg wrote:
> I'm using Swift 0.94 so I'll be happy to switch to the built-in exists
> function. However, I don't think resolves the extra copying issue. The
> reason why I had to go the way I did is that I had to make sure that
> regardless of whether a file exists or not, the Swift variable that
> represents it needs to be the output of some task, otherwise Swift
> can't track dependencies on it. The only way I could think of to
> achieve this while, making sure that the file associated with the
> Swift-visible variable had the right contents, was to copy the data
> from the original to the Swift-visible file. However Swift then copies
> the file back to the original since I gave them the same names. 

Ok, so you still need the ability to derive things from the existing
files that might be different from what was derived before.

I suggest the following:

file newOrOld; // without a mapper

file old <"/old/work/dir/xyz">;

if (exists(old) {
  newOrOld = old; // will not do a copy, but alias newOrOld to old
}
else {
  file new <"work/dir/xyz">;
  new = makeNew(...);
  newOrOld = new; // will also not do a copy, but the result will be in
work/dir/xzy
}

// now newOrOld is either /old/work/dir/xyz or work/dir/xyz

Mihael