On 05/21/2016 03:36 PM, chmike wrote:
Note however that it doesn't work with immutable. It only works with
constant. I guess this is because immutable is "stronger" than const. I
determined that only const was supported by looking at Rebindable's code.
Here is the code that finally works as I want. The flyweight pattern is
thus well supported with the exception that switch can't be used.
using static functions to get the Infos.one also allow to implement lazy
object instantiation.
[...]
I wasn't indeed using Rebindable correctly and it support only const
objects, not immutable objects.
I think your conclusion is wrong. Works fine if you add a couple
`immutable`s (and change one `IInfo` to `Info`):
----
import std.stdio;
import std.typecons;
interface IInfo {
string toString() const;
}
alias Rebindable!(immutable IInfo) Info; // Compiles just fine.
class Infos {
static class Obj : IInfo
{
this(string msg) immutable { this.msg = msg; }
private string msg;
override string toString() const { return msg; }
}
static Info one()
{
static auto x = Info(new immutable Obj("I'm one"));
return x;
}
static Info two()
{
static auto x = Info(new immutable Obj("I'm two"));
return x;
}
}
void main()
{
Info x1;
Info x2 = Infos.one;
assert(x1 is null);
assert(x2 !is null);
assert(x2 is Infos.one);
assert(x2 == Infos.one);
x1 = x2;
assert(x1 is x2);
assert(x1 == x2);
assert(x1 is Infos.one);
assert(x1 == Infos.one);
writeln(x1);
Info x3 = Info(new immutable Infos.Obj("I'm one"));
assert(x1 !is x3);
assert(x1 != x3); // Because there is no opEqual for deep equality test
Info
o1 = new immutable Infos.Obj("I'm one"),
o2 = new immutable Infos.Obj("I'm one");
assert(o1 !is o2);
assert(o1 != o2); // What I need for the flyweight pattern
/* -- Doesn't compile : x1 is not a string or integral value
switch(x1)
{
case Infos.one: writeln("case Infos.one"); break;
default: writeln("default"); break;
}
*/
}
----
I thought marking the constructor `pure` would make it possible to
implicitly convert a mutable `new` expression to immutable, but I
couldn't get that to work. That would avoid all those `immutable`s. I'm
probably forgetting something here.
