Got the following source:

class A {
    d: [String:(A)]

    public function foo(mut this) throws {
        .d.set("this", (this,))
    }
}

function main() {
    let d: [String:(A)] = [:]
    mut a = A(d)
    a.foo()
    println("OK")
}

Get the error:

Building: 1/4 (jakt__prelude__prelude.cpp)
Building: 2/4 (test.cpp)
build/test.cpp:29:58: error: no viable conversion from 'Tuple<Jakt::A>' to 'Tuple<AK::NonnullRefPtr<Jakt::A>>'
TRY((((((*this).d)).set(Jakt::DeprecatedString("this"sv),(Tuple{*this})))));
                                                         ^~~~~~~~~~~~~~
/home/hugh/src/osdev/jakt//runtime/AK/Try.h:28:39: note: expanded from macro 'TRY'
            auto _temporary_result = (expression));                                                  \
                                      ^~~~~~~~~~
/home/hugh/src/osdev/jakt//runtime/AK/Diagnostics.h:21:5: note: expanded from macro 'AK_IGNORE_DIAGNOSTIC'
    statement;                                \
    ^~~~~~~~~
/home/hugh/src/osdev/jakt//runtime/AK/Tuple.h:20:5: note: candidate inherited constructor not viable: no known conversion from 'Tuple<Jakt::A>' to 'AK::NonnullRefPtr<Jakt::A> &&' for 1st argument
    Tuple(T&& value)
    ^
/home/hugh/src/osdev/jakt//runtime/AK/Tuple.h:118:33: note: constructor from base class 'Tuple<AK::NonnullRefPtr<Jakt::A>>' inherited here
    using Detail::Tuple<Ts...>::Tuple;
                                ^
/home/hugh/src/osdev/jakt//runtime/AK/Tuple.h:26:5: note: candidate inherited constructor not viable: no known conversion from 'Tuple<Jakt::A>' to 'const AK::NonnullRefPtr<Jakt::A> &' for 1st argument
    Tuple(T const& value)
    ^
/home/hugh/src/osdev/jakt//runtime/AK/Tuple.h:118:33: note: constructor from base class 'Tuple<AK::NonnullRefPtr<Jakt::A>>' inherited here
    using Detail::Tuple<Ts...>::Tuple;
                                ^
/home/hugh/src/osdev/jakt//runtime/AK/Tuple.h:121:5: note: candidate constructor not viable: no known conversion from 'Tuple<Jakt::A>' to 'AK::Tuple<AK::NonnullRefPtr<Jakt::A>> &&' for 1st argument
    Tuple(Tuple&& other)
    ^
/home/hugh/src/osdev/jakt//runtime/AK/Tuple.h:126:5: note: candidate constructor not viable: no known conversion from 'Tuple<Jakt::A>' to 'const AK::Tuple<AK::NonnullRefPtr<Jakt::A>> &' for 1st argument
    Tuple(Tuple const& other)
    ^
/home/hugh/src/osdev/jakt//runtime/Builtins/Dictionary.h:66:39: note: passing argument to parameter 'value' here
    ErrorOr<void> set(K const& key, V value)
                                      ^
Building: 3/4 (jakt__prelude__iteration.cpp)
In file included from build/test.cpp:1:
In file included from build/test.h:2:
In file included from build/__unified_forward.h:2:
In file included from /home/hugh/src/osdev/jakt//runtime/lib.h:44:
/home/hugh/src/osdev/jakt//runtime/AK/Tuple.h:27:11: error: call to implicitly-deleted copy constructor of 'Jakt::A'
        : value(value)
          ^     ~~~~~
build/test.cpp:29:59: note: in instantiation of member function 'AK::Detail::Tuple<Jakt::A>::Tuple' requested here
TRY((((((*this).d)).set(Jakt::DeprecatedString("this"sv),(Tuple{*this})))));
                                                          ^
build/test.h:5:11: note: copy constructor of 'A' is implicitly deleted because base class 'RefCounted<Jakt::A>' has a deleted copy constructor
class A : public RefCounted<A>, public Weakable<A> {
          ^
/home/hugh/src/osdev/jakt//runtime/AK/RefCounted.h:55:20: note: copy constructor of 'RefCounted<Jakt::A>' is implicitly deleted because base class 'AK::RefCountedBase' has a deleted copy constructor
class RefCounted : public RefCountedBase {
                   ^
/home/hugh/src/osdev/jakt//runtime/AK/RefCounted.h:17:25: note: 'RefCountedBase' has been explicitly marked deleted here
    AK_MAKE_NONCOPYABLE(RefCountedBase);
                        ^
2 errors generated.
Building: 4/4 (jakt__prelude__string.cpp)
Error: Compilation failed

Not sure on a workaround just yet.

Cheers,

Hugh