Prior to this e-mail, it wasn't clear to me that there were two
different "unowned" concepts.
+1 in favor of the rename.
--Emanuel
On Tue, Dec 29, 2015 at 3:18 PM, Michael Gottesman via swift-dev
<swift-dev@swift.org> wrote:
> One form of overloading that we currently have at the SIL level are the
> notions of the "unowned" calling convention and "unowned" the variable
> ownership convention.
>
> For those who are unfamiliar with the unowned calling convention consider the
> following:
>
> @tmp : $@convention(thin) (@owned Array<Double>, Array<Double>, Int, Int) ->
> Array<Double>
>
> In this case the first parameter is passed in @owned (i.e. +1) and the second
> parameter is passed in as "unowned". Unowned is a form of +0 parameter
> passing that essentially means that the callee needs to take ownership of the
> value (ideally) before performing any side-effect having operations.
>
> Overloading the term "unowned" in this way is confusing for new people at the
> SIL level. I would like to propose that we rename the unowned calling
> convention to something else (since unowned the variable ownership convention
> corresponds to a swift level concept that will be more difficult to change).
> Additionally no matter what we do, we should annotate "unowned" parameters
> and return values with an appropriate @"..." sigil to make it absolutely
> clear visually what the convention is.
>
> In terms of names, I am partial to the name "immediate". My reasoning for
> using the term immediate is related to SGFContext in SILGen. In SILGen, there
> are three types of desired transfers defined by the DesiredTransfer enum.
>
> enum DesiredTransfer {
> PlusOne,
> ImmediatePlusZero,
> GuaranteedPlusZero,
> };
>
> PlusOne refers to @owned, GuaranteedPlusZero refers to @guaranteed, and if my
> memory is correct, ImmediatePlusZero refers to unowned. It seems natural to
> me to choose immediate for the name of the convention to match the
> terminology in SGFContext.
>
> Comments, flames, etc?
>
> Michael
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