import mir.conv: to;

alias orElse(alias fun) = visit!(some!"a", none!fun);
alias errToString = orElse!(to!string);

// can any other type including integer enum
@reflectErr
static struct ErrorInfo {
    string msg;
    auto toString() const { return msg; }
}

alias V = Variant!(Err!string, ErrorInfo, Exception, long, double);
alias R = typeof(errToString(V.init));

static assert(is(R == Variant!(string, long, double)), R.stringof);

{
    V v = 1;
    assert(v.isOk);
    assert(errToString(v) == 1);
}

{
    V v = 1.0;
    assert(v.isOk);
    assert(errToString(v) == 1.0);
}

{
    V v = ErrorInfo("msg");
    assert(!v.isOk);
    assert(errToString(v) == "msg");
}

{
    V v = "msg".err;
    assert(!v.isOk);
    assert(errToString(v) == "msg");
}

{
    V v = new Exception("msg"); enum line = __LINE__;
    assert(!v.isOk);
    assert(errToString(v) == "object.Exception@" ~ __FILE__ ~ "(" ~ line.stringof ~ "): msg");
}