An unboxed mutable array. An array is created with a given length and capacity. Length is the number of valid elements in the array. Capacity is the maximum number of elements that the array can be expanded to without having to reallocate the memory.

The elements in the array can be mutated in-place without changing the reference (constructor). However, the length of the array cannot be mutated in-place. A new array reference is generated when the length changes. When the length is increased (upto the maximum reserved capacity of the array), the array is not reallocated and the new reference uses the same underlying memory as the old one.

Several routines in this module allow the programmer to control the capacity of the array. The programmer can control the trade-off between memory usage and performance impact due to reallocations when growing or shrinking the array.

Allocates an empty unpinned array that can hold count items. The memory of the array is uninitialized.

Allocates an empty pinned array that can hold count items. The memory of the array is uninitialized and the allocation is aligned as per the Unboxed instance of the type.

Create a MutArray from the first N elements of a list. The array is allocated to size N, if the list terminates before N elements then the array may hold less than N elements.

Create a MutArray from a list. The list must be of finite size.

writeN n folds a maximum of n elements from the input stream to an MutArray.

>>> writeN = MutArray.writeNWith MutArray.newPinned
>>> writeN n = Fold.take n (MutArray.writeNUnsafe n)
>>> writeN n = MutArray.writeAppendN n (MutArray.newPinned n)

Fold the whole input to a single array.

Same as writeWith using an initial array size of arrayChunkBytes bytes rounded up to the element size.

Caution! Do not use this on infinite streams.

The array is mutated to append an additional element to it. If there is no reserved space available in the array then it is reallocated to double the original size.

This is useful to reduce allocations when appending unknown number of elements.

Note that the returned array may be a mutated version of the original array.

>>> snoc = MutArray.snocWith (* 2)

Performs O(n * log n) copies to grow, but is liberal with memory allocation.

Append n elements to an existing array. Any free space left in the array after appending n elements is lost.

>>> writeAppendN n initial = Fold.take n (MutArray.writeAppendNUnsafe n initial)

append action mutates the array generated by action to append the input stream. If there is no reserved space available in the array it is reallocated to double the size.

Note that the returned array may be a mutated version of original array.

>>> writeAppend = MutArray.writeAppendWith (* 2)

O(1) Write the given element at the given index in the array. Performs in-place mutation of the array.

>>> putIndex ix arr val = MutArray.modifyIndex ix arr (const (val, ()))
>>> f = MutArray.putIndices
>>> putIndex ix arr val = Stream.fold (f arr) (Stream.fromPure (ix, val))

O(1) Lookup the element at the given index. Index starts from 0.

Convert a MutArray into a list.

Unfold an array into a stream.

Unfold an array into a stream in reverse order.

Cast an array having elements of type a into an array having elements of type b. The length of the array should be a multiple of the size of the target element otherwise Nothing is returned.

Cast an MutArray a into an MutArray Word8.

O(1) Get the length of the array i.e. the number of elements in the array.

Note that byteLength is less expensive than this operation, as length involves a costly division operation.

A type implementing the Unbox interface supplies operations for reading and writing the type from and to a mutable byte array (an unboxed representation of the type) in memory. The read operation peekByteIndex deserializes the boxed type from the mutable byte array. The write operation pokeByteIndex serializes the boxed type to the mutable byte array.

Instances can be derived via Generic. Note that the data type must be non-recursive. Here is an example, for deriving an instance of this type class.

>>> import GHC.Generics (Generic)
>>> :{
data Object = Object
    { _int0 :: Int
    , _int1 :: Int
    } deriving Generic
:}

WARNING! Generic deriving hangs for recursive data types.

>>> import Streamly.Data.Array (Unbox(..))
>>> instance Unbox Object

If you want to write the instance manually:

>>> :{
instance Unbox Object where
    sizeOf _ = 16
    peekByteIndex i arr = do
        x0 <- peekByteIndex i arr
        x1 <- peekByteIndex (i + 8) arr
        return $ Object x0 x1
    pokeByteIndex i arr (Object x0 x1) = do
        pokeByteIndex i arr x0
        pokeByteIndex (i + 8) arr x1
:}