49 ms·

It just means you don't have to special case any particular scenario such as array-of-array, it's no different than array-of-whatever. Also jagged arrays form a

It just means you don't have to special case any particular scenario such as array-of-array, it's no different than array-of-whatever. Also jagged arrays form a complication. But even for the simple case of large non-jagged arrays: In the situation where you needed this perf gain as a developer you would still need to be able to specify the order e.g. row-major or column-major, since the VM won't know your access pattern. So if you make your own matrix class you would be better off storing a flat array yourself and doing the access arithmetic yourself like index = y*cols + x. It would be a pretty cumbersome API in Java if they had this in the declaration api and you declared double[100][100] how would you declare whether that 10k flat array is row major or column major? If the VM gets it wrong for your access pattern then a lot of the perf gain from fewer pointer indirections will be eaten by cache misses from looking in the wrong order.

samus 3y ago
This information could be made part of the type of the array. Bases on the type, Java could then compute the proper index.
- alkonaut 3y ago
  Yes, but you'd have a whole set of additional data (number of dimensions e.g. 2 and then the order of access for those dimensions). And that would affect the size of every array instance, which is something you really don't want. Or the compiler would need to keep track of it on the type level so that a row-major array can't be passed where a column major is expected etc. In any case it would really make the APIs overly complicated.
  - samus 3y ago
    It would be 4 byte more per array for metadata, plus the sizes. It would actually require less memory than ragged arrays, which have to record the size in each subarray. API complexity could be handled by a polymorphism mechanism to make it possible to write code that is generic regarding row/column access order.

samus 3y ago

This information could be made part of the type of the array. Bases on the type, Java could then compute the proper index.

alkonaut 3y ago
Yes, but you'd have a whole set of additional data (number of dimensions e.g. 2 and then the order of access for those dimensions). And that would affect the size of every array instance, which is something you really don't want. Or the compiler would need to keep track of it on the type level so that a row-major array can't be passed where a column major is expected etc. In any case it would really make the APIs overly complicated.
- samus 3y ago
  It would be 4 byte more per array for metadata, plus the sizes. It would actually require less memory than ragged arrays, which have to record the size in each subarray. API complexity could be handled by a polymorphism mechanism to make it possible to write code that is generic regarding row/column access order.