Make primitive vectors nominally roled #316
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lehins
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Jun 13, 2020
Bodigrim
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Jun 13, 2020
| @@ -137,6 +137,9 @@ module Data.Vector.Primitive ( | |||
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| -- ** Other vector types | |||
| G.convert, | |||
| #if __GLASGOW_HASKELL__ >= 708 | |||
| unsafeCoerceVector, | |||
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Having conditional API is likely to make lifes of downstream dependencies more difficult. It may be better to export unsafeCoerceVector unconditionally and define it for old GHCs without Coercible constraint.
Data/Vector/Primitive.hs
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| type role Vector representational | ||
| type role Vector nominal | ||
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| -- | /O(1)/ Unsafely coerce a mutable vector from one element type to another, |
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"a mutable" -> "an immutable"
| `type role Vector nominal` (previously, it was `phantom`). | ||
| for `Data.Vector.Primitive.Mutable.MVector` is now | ||
| `type role MVector nominal nominal` (previous, both arguments were | ||
| `phantom`). |
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"for" -> "For" (or preferably put "The role signature for" before)
"previous" -> "previously".
Bodigrim
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Data/Vector/Primitive.hs
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| -- underlying pointer and does not modify the elements. | ||
| -- | ||
| -- While it guarantees that elements of vector are representationally | ||
| -- equal it doesn't guarantee that 'Prim' instances are memory-compatible. |
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This is a subtle subject, and an unprepared reader may be well confused how types could happen to be "representationally equal", but not "memory-compatible". Here is my take (still far from perfect):
"Coerce a vector to another vector, when types of underlying elements are 'Coercible' to each other (e. g., newtypes). This is unsafe, because 'Prim' instances of newtypes can potentially still have different memory representations."
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Reasoning is identical to one for storable vectors. See discussion in haskell#224, and PR haskell#235. Fixes haskell#277
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Bodigrim
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# Changes in version 0.13.0.0
* `mkType` from `Data.Vector.Generic` is deprecated in favor of
`Data.Data.mkNoRepType`
* The role signatures on several `Vector` types were too permissive, so they
have been tightened up:
* The role signature for `Data.Vector.Mutable.MVector` is now
`type role MVector nominal representational` (previously, both arguments
were `phantom`). [#224](haskell/vector#224)
* The role signature for `Data.Vector.Primitive.Vector` is now
`type role Vector nominal` (previously, it was `phantom`).
The role signature for `Data.Vector.Primitive.Mutable.MVector` is now
`type role MVector nominal nominal` (previously, both arguments were
`phantom`). [#316](haskell/vector#316)
* The role signature for `Data.Vector.Storable.Vector` is now
`type role Vector nominal` (previous, it was `phantom`), and the signature
for `Data.Vector.Storable.Mutable.MVector` is now
`type role MVector nominal nominal` (previous, both arguments were
`phantom`). [#235](haskell/vector#235)
We pick `nominal` for the role of the last argument instead of
`representational` since the internal structure of a `Storable` vector is
determined by the `Storable` instance of the element type, and it is not
guaranteed that the `Storable` instances between two representationally
equal types will preserve this internal structure. One consequence of this
choice is that it is no longer possible to `coerce` between
`Storable.Vector a` and `Storable.Vector b` if `a` and `b` are nominally
distinct but representationally equal types. We now provide
`unsafeCoerce{M}Vector` and `unsafeCast` functions to allow this (the onus
is on the user to ensure that no `Storable` invariants are broken when
using these functions).
* Methods of type classes `Data.Vector.Generic.Mutable.MVector` and
`Data.Vector.Generic.Vector` use concrete monads (`ST`, etc) istead of being
polymorphic (`PrimMonad`, etc). [#335](haskell/vector#335).
This makes it possible to derive `Unbox` with:
* `GeneralizedNewtypeDeriving`
* via `UnboxViaPrim` and `Prim` instance
* via `As` and `IsoUnbox` instance: [#378](haskell/vector#378)
* Add `MonadFix` instance for boxed vectors: [#312](haskell/vector#312)
* Re-export `PrimMonad` and `RealWorld` from mutable vectors:
[#320](haskell/vector#320)
* Add `maximumOn` and `minimumOn`: [#356](haskell/vector#356)
* The functions `scanl1`, `scanl1'`, `scanr1`, and `scanr1'` for immutable
vectors are now defined when given empty vectors as arguments,
in which case they return empty vectors. This new behavior is consistent
with the one of the corresponding functions in `Data.List`.
Prior to this change, applying an empty vector to any of those functions
resulted in an error. This change was introduced in:
[#382](haskell/vector#382)
* Change allocation strategy for `unfoldrN`: [#387](haskell/vector#387)
* Remove `CPP` driven error reporting in favor of `HasCallStack`:
[#397](haskell/vector#397)
* Remove redundant `Storable` constraints on to/from `ForeignPtr` conversions:
[#394](haskell/vector#394)
* Add `unsafeCast` to `Primitive` vectors: [#401](haskell/vector#401)
* Make `(!?)` operator strict: [#402](haskell/vector#402)
* Add `readMaybe`: [#425](haskell/vector#425)
* Add `groupBy` and `group` for `Data.Vector.Generic` and the specialized
version in `Data.Vector`, `Data.Vector.Unboxed`, `Data.Vector.Storable` and
`Data.Vector.Primitive`. [#427](haskell/vector#427)
* Add `toArraySlice` and `unsafeFromArraySlice` functions for conversion to and
from the underlying boxed `Array`: [#434](haskell/vector#434)
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Reasoning is identical to one for storable vectors. See discussion in #224, and
PR #235.
Fixes #277