[swift-evolution] Pitch: Improved Swift pointers
kelvin13ma at gmail.com
Mon Jul 17 23:59:04 CDT 2017
I’ve drafted a new version of the unsafe pointer proposal based on feedback
I’ve gotten from this thread. You can read it here
Swift’s pointer types are an important interface for low-level memory
manipulation, but the current API design is not very safe, consistent, or
convenient. Many memory methods demand a capacity: or count: argument,
forcing the user to manually track the size of the memory block, even
though most of the time this is either unnecessary, or redundant as buffer
pointers track this information natively. In some places, this design turns
UnsafePointers into outright *Dangerous*Pointers, leading users to believe
that they have allocated or freed memory when in fact, they have not.
The current API suffers from inconsistent naming, poor usage of default
argument values, missing methods, and excessive verbosity, and encourages
excessively unsafe programming practices. This proposal seeks to iron out
these inconsistencies, and offer a more convenient, more sensible, and less
bug-prone API for Swift pointers.
The previous draft
<https://gist.github.com/kelvin13/a9c033193a28b1d4960a89b25fbffb06> of this
proposal was relatively source-breaking, calling for a separation of
functionality between singular pointer types and vector (buffer) pointer
types. This proposal instead separates functionality between
internally-tracked length pointer types and externally-tracked length
pointer types. This results in an equally elegant API with about one-third
less surface area.
On Wed, Jul 12, 2017 at 3:16 PM, Taylor Swift <kelvin13ma at gmail.com> wrote:
> Hi all, I’ve written up a proposal to modify the unsafe pointer API for
> greater consistency, safety, and ease of use.
> Swift currently offers two sets of pointer types — singular pointers such
> as UnsafeMutablePointer, and vector (buffer) pointers such as
> UnsafeMutable*Buffer*Pointer. This implies a natural separation of tasks
> the two kinds of pointers are meant to do. For example, buffer pointers
> implement Collection conformance, while singular pointers do not.
> However, some aspects of the pointer design contradict these implied
> roles. It is possible to allocate an arbitrary number of instances from a
> type method on a singular pointer, but not from a buffer pointer. The
> result of such an operation returns a singular pointer, even though a
> buffer pointer would be more appropriate to capture the information about
> the *number* of instances allocated. It’s possible to subscript into a
> singular pointer, even though they are not real Collections. Some parts
> of the current design turn UnsafePointers into downright *Dangerous*Pointers,
> leading users to believe that they have allocated or freed memory when in
> fact, they have not.
> This proposal seeks to iron out these inconsistencies, and offer a more
> convenient, more sensible, and less bug-prone API for Swift pointers.
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