| Copyright | (c) Roman Leshchinskiy 2009-2010 |
|---|---|
| License | BSD-style |
| Maintainer | Roman Leshchinskiy <rl@cse.unsw.edu.au> |
| Stability | experimental |
| Portability | non-portable |
| Safe Haskell | None |
| Language | Haskell2010 |
Data.Vector.Storable.Mutable
Description
Mutable vectors based on Storable.
Synopsis
- data MVector s a = MVector ! Int !( ForeignPtr a)
- type IOVector = MVector RealWorld
- type STVector s = MVector s
- class Storable a
- length :: Storable a => MVector s a -> Int
- null :: Storable a => MVector s a -> Bool
- slice :: Storable a => Int -> Int -> MVector s a -> MVector s a
- init :: Storable a => MVector s a -> MVector s a
- tail :: Storable a => MVector s a -> MVector s a
- take :: Storable a => Int -> MVector s a -> MVector s a
- drop :: Storable a => Int -> MVector s a -> MVector s a
- splitAt :: Storable a => Int -> MVector s a -> ( MVector s a, MVector s a)
- unsafeSlice :: Storable a => Int -> Int -> MVector s a -> MVector s a
- unsafeInit :: Storable a => MVector s a -> MVector s a
- unsafeTail :: Storable a => MVector s a -> MVector s a
- unsafeTake :: Storable a => Int -> MVector s a -> MVector s a
- unsafeDrop :: Storable a => Int -> MVector s a -> MVector s a
- overlaps :: Storable a => MVector s a -> MVector s a -> Bool
- new :: ( PrimMonad m, Storable a) => Int -> m ( MVector ( PrimState m) a)
- unsafeNew :: ( PrimMonad m, Storable a) => Int -> m ( MVector ( PrimState m) a)
- replicate :: ( PrimMonad m, Storable a) => Int -> a -> m ( MVector ( PrimState m) a)
- replicateM :: ( PrimMonad m, Storable a) => Int -> m a -> m ( MVector ( PrimState m) a)
- generate :: ( PrimMonad m, Storable a) => Int -> ( Int -> a) -> m ( MVector ( PrimState m) a)
- generateM :: ( PrimMonad m, Storable a) => Int -> ( Int -> m a) -> m ( MVector ( PrimState m) a)
- clone :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> m ( MVector ( PrimState m) a)
- grow :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> m ( MVector ( PrimState m) a)
- unsafeGrow :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> m ( MVector ( PrimState m) a)
- clear :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> m ()
- read :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> m a
- write :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> a -> m ()
- modify :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> a) -> Int -> m ()
- modifyM :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> m a) -> Int -> m ()
- swap :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> Int -> m ()
- exchange :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> a -> m a
- unsafeRead :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> m a
- unsafeWrite :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> a -> m ()
- unsafeModify :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> a) -> Int -> m ()
- unsafeModifyM :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> m a) -> Int -> m ()
- unsafeSwap :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> Int -> m ()
- unsafeExchange :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> a -> m a
- mapM_ :: ( PrimMonad m, Storable a) => (a -> m b) -> MVector ( PrimState m) a -> m ()
- imapM_ :: ( PrimMonad m, Storable a) => ( Int -> a -> m b) -> MVector ( PrimState m) a -> m ()
- forM_ :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> m b) -> m ()
- iforM_ :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> ( Int -> a -> m b) -> m ()
- foldl :: ( PrimMonad m, Storable a) => (b -> a -> b) -> b -> MVector ( PrimState m) a -> m b
- foldl' :: ( PrimMonad m, Storable a) => (b -> a -> b) -> b -> MVector ( PrimState m) a -> m b
- foldM :: ( PrimMonad m, Storable a) => (b -> a -> m b) -> b -> MVector ( PrimState m) a -> m b
- foldM' :: ( PrimMonad m, Storable a) => (b -> a -> m b) -> b -> MVector ( PrimState m) a -> m b
- foldr :: ( PrimMonad m, Storable a) => (a -> b -> b) -> b -> MVector ( PrimState m) a -> m b
- foldr' :: ( PrimMonad m, Storable a) => (a -> b -> b) -> b -> MVector ( PrimState m) a -> m b
- foldrM :: ( PrimMonad m, Storable a) => (a -> b -> m b) -> b -> MVector ( PrimState m) a -> m b
- foldrM' :: ( PrimMonad m, Storable a) => (a -> b -> m b) -> b -> MVector ( PrimState m) a -> m b
- ifoldl :: ( PrimMonad m, Storable a) => (b -> Int -> a -> b) -> b -> MVector ( PrimState m) a -> m b
- ifoldl' :: ( PrimMonad m, Storable a) => (b -> Int -> a -> b) -> b -> MVector ( PrimState m) a -> m b
- ifoldM :: ( PrimMonad m, Storable a) => (b -> Int -> a -> m b) -> b -> MVector ( PrimState m) a -> m b
- ifoldM' :: ( PrimMonad m, Storable a) => (b -> Int -> a -> m b) -> b -> MVector ( PrimState m) a -> m b
- ifoldr :: ( PrimMonad m, Storable a) => ( Int -> a -> b -> b) -> b -> MVector ( PrimState m) a -> m b
- ifoldr' :: ( PrimMonad m, Storable a) => ( Int -> a -> b -> b) -> b -> MVector ( PrimState m) a -> m b
- ifoldrM :: ( PrimMonad m, Storable a) => ( Int -> a -> b -> m b) -> b -> MVector ( PrimState m) a -> m b
- ifoldrM' :: ( PrimMonad m, Storable a) => ( Int -> a -> b -> m b) -> b -> MVector ( PrimState m) a -> m b
- nextPermutation :: ( PrimMonad m, Storable e, Ord e) => MVector ( PrimState m) e -> m Bool
- set :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> a -> m ()
- copy :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> MVector ( PrimState m) a -> m ()
- move :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> MVector ( PrimState m) a -> m ()
- unsafeCopy :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> MVector ( PrimState m) a -> m ()
- unsafeMove :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> MVector ( PrimState m) a -> m ()
- unsafeCast :: forall a b s. ( Storable a, Storable b) => MVector s a -> MVector s b
- unsafeFromForeignPtr :: Storable a => ForeignPtr a -> Int -> Int -> MVector s a
- unsafeFromForeignPtr0 :: Storable a => ForeignPtr a -> Int -> MVector s a
- unsafeToForeignPtr :: Storable a => MVector s a -> ( ForeignPtr a, Int , Int )
- unsafeToForeignPtr0 :: Storable a => MVector s a -> ( ForeignPtr a, Int )
- unsafeWith :: Storable a => IOVector a -> ( Ptr a -> IO b) -> IO b
Mutable vectors of
Storable
types
Mutable
Storable
-based vectors
Constructors
| MVector ! Int !( ForeignPtr a) |
Instances
The member functions of this class facilitate writing values of primitive types to raw memory (which may have been allocated with the above mentioned routines) and reading values from blocks of raw memory. The class, furthermore, includes support for computing the storage requirements and alignment restrictions of storable types.
Memory addresses are represented as values of type
, for some
Ptr
a
a
which is an instance of class
Storable
. The type argument to
Ptr
helps provide some valuable type safety in FFI code (you can't
mix pointers of different types without an explicit cast), while
helping the Haskell type system figure out which marshalling method is
needed for a given pointer.
All marshalling between Haskell and a foreign language ultimately
boils down to translating Haskell data structures into the binary
representation of a corresponding data structure of the foreign
language and vice versa. To code this marshalling in Haskell, it is
necessary to manipulate primitive data types stored in unstructured
memory blocks. The class
Storable
facilitates this manipulation on
all types for which it is instantiated, which are the standard basic
types of Haskell, the fixed size
Int
types (
Int8
,
Int16
,
Int32
,
Int64
), the fixed size
Word
types (
Word8
,
Word16
,
Word32
,
Word64
),
StablePtr
, all types from
Foreign.C.Types
,
as well as
Ptr
.
Minimal complete definition
sizeOf , alignment , ( peek | peekElemOff | peekByteOff ), ( poke | pokeElemOff | pokeByteOff )
Instances
Accessors
Length information
Extracting subvectors
Yield a part of the mutable vector without copying it. The vector must
contain at least
i+n
elements.
init :: Storable a => MVector s a -> MVector s a Source #
Drop last element of the mutable vector without making a copy. If vector is empty exception is thrown.
tail :: Storable a => MVector s a -> MVector s a Source #
Drop first element of the mutable vector without making a copy. If vector is empty exception is thrown.
take :: Storable a => Int -> MVector s a -> MVector s a Source #
Take
n
first elements of the mutable vector without making a
copy. For negative
n
empty vector is returned. If
n
is larger
than vector's length empty vector is returned,
drop :: Storable a => Int -> MVector s a -> MVector s a Source #
Drop
n
first element of the mutable vector without making a
copy. For negative
n
vector is returned unchanged and if
n
is
larger than vector's length empty vector is returned.
Arguments
| :: Storable a | |
| => Int |
starting index |
| -> Int |
length of the slice |
| -> MVector s a | |
| -> MVector s a |
Yield a part of the mutable vector without copying it. No bounds checks are performed.
unsafeInit :: Storable a => MVector s a -> MVector s a Source #
Same as
init
but doesn't do range checks.
unsafeTail :: Storable a => MVector s a -> MVector s a Source #
Same as
tail
but doesn't do range checks.
unsafeTake :: Storable a => Int -> MVector s a -> MVector s a Source #
Unsafe variant of
take
. If called with out of range
n
it will
simply create invalid slice that likely violate memory safety
unsafeDrop :: Storable a => Int -> MVector s a -> MVector s a Source #
Unsafe variant of
drop
. If called with out of range
n
it will
simply create invalid slice that likely violate memory safety
Overlapping
overlaps :: Storable a => MVector s a -> MVector s a -> Bool Source #
Check whether two vectors overlap.
Construction
Initialisation
new :: ( PrimMonad m, Storable a) => Int -> m ( MVector ( PrimState m) a) Source #
Create a mutable vector of the given length.
unsafeNew :: ( PrimMonad m, Storable a) => Int -> m ( MVector ( PrimState m) a) Source #
Create a mutable vector of the given length. The vector content is uninitialized, which means it is filled with whatever underlying memory buffer happens to contain.
Since: 0.5
replicate :: ( PrimMonad m, Storable a) => Int -> a -> m ( MVector ( PrimState m) a) Source #
Create a mutable vector of the given length (0 if the length is negative) and fill it with an initial value.
replicateM :: ( PrimMonad m, Storable a) => Int -> m a -> m ( MVector ( PrimState m) a) Source #
Create a mutable vector of the given length (0 if the length is negative) and fill it with values produced by repeatedly executing the monadic action.
generate :: ( PrimMonad m, Storable a) => Int -> ( Int -> a) -> m ( MVector ( PrimState m) a) Source #
O(n) Create a mutable vector of the given length (0 if the length is negative) and fill it with the results of applying the function to each index.
Since: 0.12.3.0
generateM :: ( PrimMonad m, Storable a) => Int -> ( Int -> m a) -> m ( MVector ( PrimState m) a) Source #
O(n) Create a mutable vector of the given length (0 if the length is negative) and fill it with the results of applying the monadic function to each index. Iteration starts at index 0.
Since: 0.12.3.0
clone :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> m ( MVector ( PrimState m) a) Source #
Create a copy of a mutable vector.
Growing
grow :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> m ( MVector ( PrimState m) a) Source #
Grow a storable vector by the given number of elements. The number must be
non-negative. Same semantics as in
grow
for generic vector.
Examples
>>>import qualified Data.Vector.Storable as VS>>>import qualified Data.Vector.Storable.Mutable as MVS>>>mv <- VS.thaw $ VS.fromList ([10, 20, 30] :: [Int])>>>mv' <- MVS.grow mv 2
Extra memory at the end of the newly allocated vector is initialized to 0
bytes, which for
Storable
instance will usually correspond to some default
value for a particular type, eg.
0
for
Int
,
False
for
Bool
,
etc. However, if
unsafeGrow
was used instead this would not have been
guaranteed and some garbage would be there instead:
>>>VS.freeze mv'[10,20,30,0,0]
Having the extra space we can write new values in there:
>>>MVS.write mv' 3 999>>>VS.freeze mv'[10,20,30,999,0]
It is important to note that the source mutable vector is not affected when the newly allocated one is mutated.
>>>MVS.write mv' 2 888>>>VS.freeze mv'[10,20,888,999,0]>>>VS.freeze mv[10,20,30]
Since: 0.5
unsafeGrow :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> m ( MVector ( PrimState m) a) Source #
Grow a vector by the given number of elements. The number must be non-negative but
this is not checked. Same semantics as in
unsafeGrow
for generic vector.
Since: 0.5
Restricting memory usage
clear :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> m () Source #
Reset all elements of the vector to some undefined value, clearing all references to external objects. This is usually a noop for unboxed vectors.
Accessing individual elements
read :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> m a Source #
Yield the element at the given position.
write :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> a -> m () Source #
Replace the element at the given position.
modify :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> a) -> Int -> m () Source #
Modify the element at the given position.
modifyM :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> m a) -> Int -> m () Source #
Modify the element at the given position using a monadic function.
Since: 0.12.3.0
swap :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> Int -> m () Source #
Swap the elements at the given positions.
exchange :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> a -> m a Source #
Replace the element at the given position and return the old element.
unsafeRead :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> m a Source #
Yield the element at the given position. No bounds checks are performed.
unsafeWrite :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> a -> m () Source #
Replace the element at the given position. No bounds checks are performed.
unsafeModify :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> a) -> Int -> m () Source #
Modify the element at the given position. No bounds checks are performed.
unsafeModifyM :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> m a) -> Int -> m () Source #
Modify the element at the given position using a monadic function. No bounds checks are performed.
Since: 0.12.3.0
unsafeSwap :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> Int -> m () Source #
Swap the elements at the given positions. No bounds checks are performed.
unsafeExchange :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> Int -> a -> m a Source #
Replace the element at the given position and return the old element. No bounds checks are performed.
Folds
mapM_ :: ( PrimMonad m, Storable a) => (a -> m b) -> MVector ( PrimState m) a -> m () Source #
O(n) Apply the monadic action to every element of the vector, discarding the results.
Since: 0.12.3.0
imapM_ :: ( PrimMonad m, Storable a) => ( Int -> a -> m b) -> MVector ( PrimState m) a -> m () Source #
O(n) Apply the monadic action to every element of the vector and its index, discarding the results.
Since: 0.12.3.0
forM_ :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> (a -> m b) -> m () Source #
O(n)
Apply the monadic action to every element of the vector,
discarding the results. It's same as the
flip mapM_
.
Since: 0.12.3.0
iforM_ :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> ( Int -> a -> m b) -> m () Source #
O(n)
Apply the monadic action to every element of the vector
and its index, discarding the results. It's same as the
flip imapM_
.
Since: 0.12.3.0
foldl :: ( PrimMonad m, Storable a) => (b -> a -> b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Pure left fold.
Since: 0.12.3.0
foldl' :: ( PrimMonad m, Storable a) => (b -> a -> b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Pure left fold with strict accumulator.
Since: 0.12.3.0
foldM :: ( PrimMonad m, Storable a) => (b -> a -> m b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Monadic fold.
Since: 0.12.3.0
foldM' :: ( PrimMonad m, Storable a) => (b -> a -> m b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Monadic fold with strict accumulator.
Since: 0.12.3.0
foldr :: ( PrimMonad m, Storable a) => (a -> b -> b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Pure right fold.
Since: 0.12.3.0
foldr' :: ( PrimMonad m, Storable a) => (a -> b -> b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Pure right fold with strict accumulator.
Since: 0.12.3.0
foldrM :: ( PrimMonad m, Storable a) => (a -> b -> m b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Monadic right fold.
Since: 0.12.3.0
foldrM' :: ( PrimMonad m, Storable a) => (a -> b -> m b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Monadic right fold with strict accumulator.
Since: 0.12.3.0
ifoldl :: ( PrimMonad m, Storable a) => (b -> Int -> a -> b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Pure left fold (function applied to each element and its index).
Since: 0.12.3.0
ifoldl' :: ( PrimMonad m, Storable a) => (b -> Int -> a -> b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Pure left fold with strict accumulator (function applied to each element and its index).
Since: 0.12.3.0
ifoldM :: ( PrimMonad m, Storable a) => (b -> Int -> a -> m b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Monadic fold (action applied to each element and its index).
Since: 0.12.3.0
ifoldM' :: ( PrimMonad m, Storable a) => (b -> Int -> a -> m b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Monadic fold with strict accumulator (action applied to each element and its index).
Since: 0.12.3.0
ifoldr :: ( PrimMonad m, Storable a) => ( Int -> a -> b -> b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Pure right fold (function applied to each element and its index).
Since: 0.12.3.0
ifoldr' :: ( PrimMonad m, Storable a) => ( Int -> a -> b -> b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Pure right fold with strict accumulator (function applied to each element and its index).
Since: 0.12.3.0
ifoldrM :: ( PrimMonad m, Storable a) => ( Int -> a -> b -> m b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Monadic right fold (action applied to each element and its index).
Since: 0.12.3.0
ifoldrM' :: ( PrimMonad m, Storable a) => ( Int -> a -> b -> m b) -> b -> MVector ( PrimState m) a -> m b Source #
O(n) Monadic right fold with strict accumulator (action applied to each element and its index).
Since: 0.12.3.0
Modifying vectors
nextPermutation :: ( PrimMonad m, Storable e, Ord e) => MVector ( PrimState m) e -> m Bool Source #
Compute the next (lexicographically) permutation of given vector in-place. Returns False when input is the last permutation
Filling and copying
set :: ( PrimMonad m, Storable a) => MVector ( PrimState m) a -> a -> m () Source #
Set all elements of the vector to the given value.
Arguments
| :: ( PrimMonad m, Storable a) | |
| => MVector ( PrimState m) a |
target |
| -> MVector ( PrimState m) a |
source |
| -> m () |
Copy a vector. The two vectors must have the same length and may not overlap.
Arguments
| :: ( PrimMonad m, Storable a) | |
| => MVector ( PrimState m) a |
target |
| -> MVector ( PrimState m) a |
source |
| -> m () |
Move the contents of a vector. The two vectors must have the same length.
If the vectors do not overlap, then this is equivalent to
copy
.
Otherwise, the copying is performed as if the source vector were
copied to a temporary vector and then the temporary vector was copied
to the target vector.
Arguments
| :: ( PrimMonad m, Storable a) | |
| => MVector ( PrimState m) a |
target |
| -> MVector ( PrimState m) a |
source |
| -> m () |
Copy a vector. The two vectors must have the same length and may not overlap. This is not checked.
Arguments
| :: ( PrimMonad m, Storable a) | |
| => MVector ( PrimState m) a |
target |
| -> MVector ( PrimState m) a |
source |
| -> m () |
Move the contents of a vector. The two vectors must have the same length, but this is not checked.
If the vectors do not overlap, then this is equivalent to
unsafeCopy
.
Otherwise, the copying is performed as if the source vector were
copied to a temporary vector and then the temporary vector was copied
to the target vector.
Unsafe conversions
unsafeCast :: forall a b s. ( Storable a, Storable b) => MVector s a -> MVector s b Source #
O(1) Unsafely cast a mutable vector from one element type to another. The operation just changes the type of the underlying pointer and does not modify the elements.
The resulting vector contains as many elements as can fit into the underlying memory block.
Raw pointers
Arguments
| :: Storable a | |
| => ForeignPtr a |
pointer |
| -> Int |
offset |
| -> Int |
length |
| -> MVector s a |
Create a mutable vector from a
ForeignPtr
with an offset and a length.
Modifying data through the
ForeignPtr
afterwards is unsafe if the vector
could have been frozen before the modification.
If your offset is 0 it is more efficient to use
unsafeFromForeignPtr0
.
unsafeFromForeignPtr0 Source #
Arguments
| :: Storable a | |
| => ForeignPtr a |
pointer |
| -> Int |
length |
| -> MVector s a |
O(1)
Create a mutable vector from a
ForeignPtr
and a length.
It is assumed the pointer points directly to the data (no offset).
Use
unsafeFromForeignPtr
if you need to specify an offset.
Modifying data through the
ForeignPtr
afterwards is unsafe if the vector
could have been frozen before the modification.
unsafeToForeignPtr :: Storable a => MVector s a -> ( ForeignPtr a, Int , Int ) Source #
Yield the underlying
ForeignPtr
together with the offset to the data
and its length. Modifying the data through the
ForeignPtr
is
unsafe if the vector could have frozen before the modification.
unsafeToForeignPtr0 :: Storable a => MVector s a -> ( ForeignPtr a, Int ) Source #
O(1)
Yield the underlying
ForeignPtr
together with its length.
You can assume the pointer points directly to the data (no offset).
Modifying the data through the
ForeignPtr
is unsafe if the vector could
have frozen before the modification.