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On the Hackernoon site Nicolò Pignatelli wrote a good guide on how to write Value objects in a good way.

This is the list you must always check it against:

• it is immutable and no setters defined;
• it reflects the semantics of the domain;
• it shows how information flows and is transformed during runtime;
• it hasn’t default or useless getter methods;
• it can be compared to other Value Objects of the - - same class by reading private properties directly

https://hackernoon.com/value-objects-like-a-pro-f1bfc1548c72

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Ross Tuck is probably one of my favourite bloggers. He doesn't publish something often (his previous post is from 2015), but when he does it's very much worth your time.

The important takeaway here isn’t “value objects, yay, inline juggling, boo!” It’s that we were able to remove several classes of errors by reducing the precision of the DateTime we were handling. If we hadn’t done that, the value object would still be handling all of these edges cases and probably failing at some of them too.

Reducing the quality of data to get a correct answer might seem counter-intuitive but it’s actually a more realistic view of the system we’re trying to model. Our computers might run in picoseconds but our business (probably) doesn’t. Plus, the computer is probably lying anyways.

http://rosstuck.com/precision-through-imprecision-improving-time-objects

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Mathias Verraes illustrates with practical examples how PHP's type system can be used when designing a system.

Below is an attempt at illustrating a design/redesign process I went through at a client, who’s started refactoring the core systems their business depends on. Design is the part of software development that is the most messy, the hardest to fit into rules or well-defined processes. In fact, while writing this post, I tweeted:

“There are surprisingly few software design books that recommend taking a walk, a shower, or a nap, as an important step.”

None of the solutions offered below should be taken as truth. I may have already changed my mind on some of them by the time you read them.

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