[Swift-devel] [Bug 291] New: Add a exists() function to test for file existence

[Ben Clifford]

> And I am emphasizing here that the optional attribute should belong to
> the data. You probably don't want to have it optional with one
> invocation and non optional with another. Given that the successful
> completion of a run requires that all invocations complete successfully,
> anything else would be silly.

maybe "optional" is not the right word. its data that needs to exist. but 
you are specifying two ways for it to exist in the scope of the current 
run: either you find it on a filesystem, or you run some program that 
outputs it. but I agree that whatever it is called, its attached to the 
data not to an invocation. it sounds a lot like the virtual data idea.

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