Working with views and values

[Vanessa McHale]

Is there any way to implement

extern
fn {a:vt@ype} as_view (a) : [ l : addr | l > null ] (a @ l | aptr(l))

extern
fn {a:vt@ype} as_value {l:addr} ((a @ l | aptr(l))) : a

?

I've tried using view@ and addr@ but it seems they're for stack
allocations. I suppose I could write my own view in place of using a @
l, but I don't see any way around addr@.

Thanks!

[Hongwei Xi]

What is aptr(l)?

Here is some code that may be helpful:

extern
fun
{a:vt0p}
ptr_alloc((*void*))
  :<> [l:agz] (a? @ l, mfree_gc_v(l) | ptr(l))
// end of [ptr_alloc]

extern
fn
{a:vt@ype}
as_view(a):
[l:addr | l > null]
(a @ l, mfree_gc_v(l) | ptr(l))

implement
{a}
as_view(x) = let
  val
  (pf,fpf|p) =
  ptr_alloc<a>()
in
  !p := x; (pf, fpf | p)
end

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[Hongwei Xi]

If you just want to pass a value via call-by-reference, you can do

fun{a:vt@ype}

foo(x: a): ... = let

   var x = x

   // now the name 'x' refers to a variable, which is a form of left-value

  // that can be passed via call-by-reference

... ...

[Vanessa McHale]

aptr(l) is an atomic pointer. I believe you can cast between prl(l) and aptr(l) though my C is not particularly good.

And thanks! I'll have a look :)

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