5 ms·

I made a comment on my understanding of the difference in implementation here: https://news.ycombinator.com/item?id=48606173 https://news.ycombinator.com/item?i

• gf000 4mo ago
  > allocation of blocks of memory on stack) Why couldn't it be done? Like sure, it won't happen in every case (e.g. too big value classes), but for a typical local variable of a value type, it's a trivial optimization to make it stack allocated. Even now it happens quite often (requires escape analysis), but the semantics change of value classes allows for it to be done "freely".
  • kuhsaft 4mo ago
    C# stackalloc returns a ‘ref struct’ which has certain restrictions and would be a Q-world type. Java chose to go with an L-world implementation where everything is still a reference type on the heap, but memory management is more efficient via flattening. That’s why it’s a ‘value class’ and not a ‘struct’. Primitive wrappers are scalarized into registers. Stack allocated value types would have different semantics and is incompatible with the L-world implementation. Sure, they could implement it, but it would be the Q-world implementation that they decided to forego. They can do automatic stack allocation for optimization via escape analysis as you mentioned. But, stackalloc is user allocated. https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/ref-struct https://learn.microsoft.com/en-us/dotnet/csharp/language-ref...