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

[Vijay Nayar]

On Saturday, 2 April 2022 at 14:35:10 UTC, Vijay Nayar wrote:
> 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"
> ```

Through sheer trial and error, I discovered that changing the 
handler arguments from `ref ubyte[]` to `const ref ubyte[]` the 
error goes away. However, I did not find any information in the 
documentation or code that made this requirement clear. It was 
basically a guess based on the fact that `string` has no trouble 
but `ubyte[]` did, and string is basically just 
`immutable(char[])`.

So far, I'm finding that learning to use `SumType` is 
significantly more cryptic than `Variant`, by a large margin. 
I'll still give it a shot of course, because I want to get past 
this problem.