Hi,
I'd like to use immutable data, but instead of a one time
constructor, I would like to `build` the data lazily, by setting
its fields separately.
In java version of protocol-buffer, there is a pattern for this
mechanism:
1. Every data class in protobuf is immutable.
2. Each data class is companioned by a Builder class, with the
same field of the immutable data class.
3. To create a data object, first create a Builder, then set the
fields when ever you want.
I want to emulate this process, but without needing to create two
classes for one data class (protobuff does this by a separate
code generating phase to generate both classes from a data format
file).
What is the idiomatic approach to do this in D?
if I define a class with immutable fields, like
```d
class A {
immutable int id;
immutable B b;
}
```
should I use a template to generate the companion Builder class,
or is there another aproach?
