Can std.variant be used with std.container.rbtree?

[Vijay Nayar]

On Saturday, 2 April 2022 at 10:04:49 UTC, vit wrote:
> Try use ```std.sumtype```.

I'm playing with SumType to see how it works, and I must be doing 
something silly, because it fails to compile with the first 
example type I attempted. Consider the following:

```d
import std.sumtype;
import std.algorithm : cmp;

alias VarType = SumType!(double, ubyte[]);

int opCmp(const ref VarType v1, const ref VarType v2) {
   alias doMatch = tryMatch!(
       (ref ubyte[] _1, ref ubyte[] _2) => cmp(_1, _2),
       (_1, _2) => _1 < _2 ? -1 : (_2 < _1 ? 1 : 0));
   return doMatch(v1, v2);
}

void main() {
   VarType b1 = cast(ubyte[]) [0x01, 0x02, 0x03];
   VarType b2 = cast(ubyte[]) [0x01, 0x02, 0x04];
   b1 > b2;
}
```

The `tryMatch` method fails to compile, and instead I get the 
following error:
```d
/dlang/dmd/linux/bin64/../../src/phobos/std/sumtype.d(2004): 
Error: static assert:  "`handlers[0]` of type `int function(ref 
ubyte[] _1, ref ubyte[] _2) pure nothrow @nogc @safe` never 
matches"
/dlang/dmd/linux/bin64/../../src/phobos/std/sumtype.d(1739):      
   instantiated from here: `matchImpl!(const(SumType!(double, 
ubyte[])), const(SumType!(double, ubyte[])))`
onlineapp.d(10):        instantiated from here: 
`tryMatch!(const(SumType!(double, ubyte[])), 
const(SumType!(double, ubyte[])))`
```

I'm not super sure why this handler would not match. If I do 
simple types like `double` or `int` it works, it even works with 
`string`, but the moment I include `ubyte[]`, it no longer 
compiles. In this example, I eliminated all other array types 
aside from `ubyte[]`, so there should be no conflicts in theory.