Setting field of struct object

[Joel via Digitalmars-d-learn]

I've been watching a video (YouTube - "Pipeline-oriented 
programming - Scott Wlaschin - NDC Porto 2023") with something 
like the following code. This only sets the first method call, so 
I'm wanting to know how to make this work, for the subsequent 
methods.

```d
import std;
struct Person {
    string name, email;
    ulong age;
    auto withName(string name) { this.name=name; return this; }
    auto withEmail(string email) { this.email=email; return this; 
}
    auto withAge(ulong age) { this.age=age; return this; }
}

void main() {
    Person p;
    p.withName("Tom").withEmail("joel...@gmail.com").withAge(44);
    writeln(p);
}
```