Invalid bounding interval [, ]

[bearophile]

C:

> I want to fill a ubyte array with random data.

In D ubytes are not char, they are two different types. So if you want ubytes, then use ubytes:
uniform!("[]")(ubyte.min, ubyte.max)


Regarding your error, a reduced test case:

import std.random: uniform;
void main() {
    uniform!("[]")(char.min, char.max);
    uniform!("(]")(char.min, char.max);
}

Bye,
bearophile