D 2021-10-07T06:44:23.183
L get\sthe\saddress\sof\sa\sfield
U admin
W 1072
<h3>Getting the address of a field... when the field might be a property function</h3>

<div class="language-d"><verbatim>
struct S {
    private int n;
    ref int prop() return { return n; }
}

auto ref eval(T)(auto ref T t) { return t; }

/// How do we get a pointer to n?
unittest {
    auto s = S(13);
    auto p1 = &s.prop;              // wrong
    auto p2 = &(s.prop);            // wrong
    // auto p3 = &(x => x)(s.prop); // error
    int* p4 = &eval(s.prop);        // eval helper

    assert(typeof(p1).stringof == "int delegate() ref return");
    assert(typeof(p2).stringof == "int delegate() ref return");
    assert(p2() == 13);

    (*p4)++;
    p4[0]++;

    assert(p1() == 15);

    // technically works, but requires this code to be in the same module as
    // S's definition, and requires us to know the name of the real variable.
    // what if S is a user-provided type?
    int* p5 = &s.n;

    // eval works for fields as well
    int* p6 = &eval(s.n);
}
</verbatim></div>

[https://forum.dlang.org/post/sjkh5i$2p17$1@digitalmars.com|Discussion]
Z 8ef36b36eb939a4eedc1c67912356534