[swift-evolution] SE-1084 (B): buffer pointer partial initialization API

Ben Cohen ben_cohen at apple.com
Wed Oct 11 15:42:26 CDT 2017

> On Oct 11, 2017, at 1:15 PM, Kelvin Ma via swift-evolution <swift-evolution at swift.org> wrote:
> there is no way to allow one-sided subscripting, but disallow two-sided subscripting for the memory API

One-sided subscripting is just shorthand for “from here to the end” (or from the start to/through here). If a one-sided subscript is just shorthand for a two-sided subscript there cannot be a circumstance where one is allowed but not the other. This kind of rule should be consistent throughout the library.

If a “from:” argument, similarly, means “write from here up to the end” (and no further, it’s reasonable to assume, if we’re talking about collections) then x.foo(from: i) is similar to saying x[i…].foo(), which in turn is similar to saying x[5..<x.endIndex].foo()

Do you feel like a “from:” argument avoids implying there is a specific end point to the operation? That is, it might not get as far as x.endIndex if it runs out of stuff to write. Whereas x[i..<x.endIndex].foo() more implies “this will definitively replace the entire range from i to the end”?

(with x[i…].foo() living in an unpleasant grey-area)

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