This code doesn't work:
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auto ref run(F, Args...)(F dg, auto ref Args args)
{
    return dg(args);
}
auto makeClosure(alias func, Args...)(auto ref Args args)
{
    auto fptr = args[0].funcptr;
    return {
        // !!!!! Assertion failure !!!!!
        assert(args[0].funcptr is fptr);
        return func(args);
    };
}
auto test(F, Args...)(F dg, auto ref Args args)
{
    return makeClosure!run(dg, args);
}
void main()
{
    auto t = test( delegate ()=> 10 );
    assert(t() == 10);
}
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dmd -debug -g -run main.d
-------------------
core.exception.AssertError@main.d(9): Assertion failure
----------------
0x004029B3 in _d_assertp at ...\src\core\exception.d(436)
0x0040225B in _Dmain at main.d(20)