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[sil] Add clarity to how load_weak [take] and store_weak effect an ob… #21985

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Jan 18, 2019
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[sil] Add clarity to how load_weak [take] and store_weak effect an ob… #21985

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[sil] Add clarity to how load_weak [take] and store_weak effect an ob…
gottesmm Jan 18, 2019
5701eb3
Update given John's feedback.
gottesmm Jan 18, 2019
3585d7d
Make text clearer.
gottesmm Jan 18, 2019
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15 changes: 14 additions & 1 deletion docs/SIL.rst
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Expand Up @@ -2827,6 +2827,13 @@ which must be an initialized weak reference. The result is value of type
``$Optional<T>``, except that it is ``null`` if the heap object has begun
deallocation.

If ``[take]`` is specified then the underlying weak reference is invalidated
implying that the weak reference count of the loaded value is decremented. If
``[take]`` is not specified then the underlying weak reference count is not
affected by this operation (i.e. it is a +0 weak ref count operation). In either
case, the strong reference count will be incremented before any changes to the
weak reference count.

This operation must be atomic with respect to the final ``strong_release`` on
the operand heap object. It need not be atomic with respect to ``store_weak``
operations on the same address.
Expand All @@ -2845,7 +2852,13 @@ Initializes or reassigns a weak reference. The operand may be ``nil``.

If ``[initialization]`` is given, the weak reference must currently either be
uninitialized or destroyed. If it is not given, the weak reference must
currently be initialized.
currently be initialized. After the evaluation:

* The value that was originally referenced by the weak reference will have
its weak reference count decremented by 1.
* If the optionally typed operand is non-nil, the strong reference wrapped in
the optional has its weak reference count incremented by 1. In contrast, the reference's
strong reference count is not touched.

This operation must be atomic with respect to the final ``strong_release`` on
the operand (source) heap object. It need not be atomic with respect to
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