unsafe package:array

Contains the various unsafe operations that can be performed on arrays.

Converts an mutable array into an immutable array. The implementation may either simply cast the array from one type to the other without copying the array, or it may take a full copy of the array. Note that because the array is possibly not copied, any subsequent modifications made to the mutable version of the array may be shared with the immutable version. It is safe to use, therefore, if the mutable version is never modified after the freeze operation. The non-copying implementation is supported between certain pairs of array types only; one constraint is that the array types must have identical representations. In GHC, The following pairs of array types have a non-copying O(1) implementation of unsafeFreeze. Because the optimised versions are enabled by specialisations, you will need to compile with optimisation (-O) to get them.

• IOUArray -> UArray
• STUArray -> UArray
• IOArray -> Array
• STArray -> Array

Builds a new array, with every element initialised to an undefined value. The first and second element of the tuple specifies the lowest and highest index, respectively.

Converts an immutable array into a mutable array. The implementation may either simply cast the array from one type to the other without copying the array, or it may take a full copy of the array. Note that because the array is possibly not copied, any subsequent modifications made to the mutable version of the array may be shared with the immutable version. It is only safe to use, therefore, if the immutable array is never referenced again in this thread, and there is no possibility that it can be also referenced in another thread. If you use an unsafeThawwriteunsafeFreeze sequence in a multi-threaded setting, then you must ensure that this sequence is atomic with respect to other threads, or a garbage collector crash may result (because the write may be writing to a frozen array). The non-copying implementation is supported between certain pairs of array types only; one constraint is that the array types must have identical representations. In GHC, The following pairs of array types have a non-copying O(1) implementation of unsafeThaw. Because the optimised versions are enabled by specialisations, you will need to compile with optimisation (-O) to get them.

• UArray -> IOUArray
• UArray -> STUArray
• Array -> IOArray
• Array -> STArray