Re: partially mutable immutable type problem, crazy idea

[Yuxuan Shui via Digitalmars-d]

On Wednesday, 9 May 2018 at 00:58:51 UTC, jmh530 wrote:

On Tuesday, 8 May 2018 at 22:31:10 UTC, Yuxuan Shui wrote:

snip]


This doesn't compile for me on run.dlang.io:

onlineapp.d(22): Error: template onlineapp.f cannot deduce 
function from argument types !()(B), candidates are:

onlineapp.d(1):onlineapp.f(T)(immutable T a)


Not supposed to. Was proposing an (crazy) idea here.

Re: partially mutable immutable type problem, crazy idea

[jmh530 via Digitalmars-d]

On Tuesday, 8 May 2018 at 22:31:10 UTC, Yuxuan Shui wrote:

snip]


This doesn't compile for me on run.dlang.io:

onlineapp.d(22): Error: template onlineapp.f cannot deduce 
function from argument types !()(B), candidates are:

onlineapp.d(1):onlineapp.f(T)(immutable T a)

Re: partially mutable immutable type problem, crazy idea

[Yuxuan Shui via Digitalmars-d]

After watching the DConf 2018 video, I came up with this wild 
idea:


auto f(T)(immutable T a) {
// If T is a aggregate type, and I only use (directly
// or indirectly) the immutable fields of T,
// Then it should be OK to call f() with a partially mutable 
type

return a.x+1;
}

void main() {
struct A {
int x;
}
A a;
immutable(A) b;
f(a); // <- not fine
f(b); // <- fine

class B {
immutable int x = 10;
double f;
}
auto c = new B;
f(c); // <- fine too
}

I think this should solve the reference counting an immutable 
object, no? To f(), T will just looks like a normal immutable, 
uncopyable (because copying means modifying the reference 
counter) type