RE: [Caml-list] How much optimized is the 'a option type ?

["Jon Harrop" <jon@ffconsultancy.com>]

Yotam wrote:
> Just to clarify, by value types you mean stuff allocated on the stack,
right?

A value type is just an unboxed type like a C struct. A local variable of a
value type is stored on the stack. A field inside a heap-allocated object
that is a value type is stored inside the object and not in a separate
object. An array of value types is a single contiguous block of memory with
no pointers (e.g. an array of complex numbers).

With value types you can almost completely avoid the garbage collector by
replacing pointers with indices into an array of value types that acts as a
pool allocator. This can be useful for avoiding GC latency and for
optimizing for collections that violate the generational hypothesis (e.g.
long-lived Sets and Maps).

In HLVM, tuples were value types. For example, an (int * float) array is
represented as a single contiguous block of memory. In constrast, OCaml
represents this is an array of pointers to pairs where the second element is
another pointer to a boxed float.

Value types and reified generics permit very efficient hash tables. For
example, the Dictionary<int, float> type on .NET does not contain any
pointers.

Cheers,
Jon.