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[Docs] Clarify partial_apply's ownership of @inout_aliasable arguments. #26523

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Aug 10, 2019
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[Docs] Clarify partial_apply's ownership of @inout_aliasable arguments. #26523

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20 changes: 13 additions & 7 deletions docs/SIL.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -3484,13 +3484,14 @@ has an escaping function type (not ``[on_stack]``) the closure context will be
allocated with retain count 1 and initialized to contain the values ``%1``,
``%2``, etc. The closed-over values will not be retained; that must be done
separately before the ``partial_apply``. The closure does however take ownership
of the partially applied arguments; when the closure reference count reaches
zero, the contained values will be destroyed. If the ``partial_apply`` has a
``@noescape`` function type (``partial_apply [on_stack]``) the closure context
is allocated on the stack and initialized to contain the closed-over values. The
closed-over values are not retained, lifetime of the closed-over values must be
managed separately. The lifetime of the stack context of a ``partial_apply
[on_stack]`` must be terminated with a ``dealloc_stack``.
of the partially applied arguments (except for ``@inout_aliasable`` parameters);
when the closure reference count reaches zero, the contained values will be
destroyed. If the ``partial_apply`` has a ``@noescape`` function type
(``partial_apply [on_stack]``) the closure context is allocated on the stack and
initialized to contain the closed-over values. The closed-over values are not
retained, lifetime of the closed-over values must be managed separately. The
lifetime of the stack context of a ``partial_apply [on_stack]`` must be
terminated with a ``dealloc_stack``.

If the callee is generic, all of its generic parameters must be bound by the
given substitution list. The arguments are given with these generic
Expand All @@ -3499,6 +3500,11 @@ type with the given substitutions applied. The generic parameters themselves
cannot be partially applied; all of them must be bound. The result is always
a concrete function.

If an address argument has ``@inout_aliasable`` convention, the closure
obtained from ``partial_apply`` will not own its underlying value.
The ``@inout_aliasable`` parameter convention is used when a ``@noescape``
closure captures an ``inout`` argument.

TODO: The instruction, when applied to a generic function,
currently implicitly performs abstraction difference transformations enabled
by the given substitutions, such as promoting address-only arguments and returns
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