pitrou commented on a change in pull request #10550:
URL: https://github.com/apache/arrow/pull/10550#discussion_r655196937
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File path: cpp/src/arrow/compute/kernels/scalar_cast_internal.cc
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@@ -255,7 +255,12 @@ static bool CanCastFromDictionary(Type::type type_id) {
void AddCommonCasts(Type::type out_type_id, OutputType out_ty, CastFunction*
func) {
// From null to this type
- DCHECK_OK(func->AddKernel(Type::NA, {null()}, out_ty, CastFromNull));
+ ScalarKernel kernel;
+ kernel.exec = CastFromNull;
+ kernel.signature = KernelSignature::Make({null()}, out_ty);
+ kernel.null_handling = NullHandling::COMPUTED_NO_PREALLOCATE;
+ kernel.mem_allocation = MemAllocation::NO_PREALLOCATE;
Review comment:
Not sure, because `MakeArrayOfNull` allocates a single
(sufficiently-sized) buffer of 0s for all array buffers. Preallocating in the
kernel execution machinery without any specific knowledge about the kernel
would allocate distinct buffers and consume more memory (though probably not
that much).
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