And when you want to make Foo no longer a primary value and instead calculated from some other field? When you want to add logging to every change of Foo? Every access? When you want to switch to having Foo's value come from a database? Web service?

Then that is when you have to change the public field to a property, with no change to calling code.

Reasons for going with a property from the start is if you a) ever use reflection (which would need to change depending on whether the storage is a public field vs a property) b) If you need to implement interfaces using the property. Reasons for going with a public field is for special cases where you know a lot about how inlining affects your performance. Typically in structs.

Since there is no more boilerplate used to write "public int Id { get; }" vs "public readonly int Id", in 99% of cases I'd choose the latter.

Then I'd change it to a property and recompile. If it's value comes from the database or a web service then nothing has to change, whatever is calling the service will invoke the constructor as always.

The only exception here is for public APIs, but that's a minority of projects.

> Then I'd change it to a property and recompile

You mean, change it to a property, then fix dozens or hundreds of references, possibly in downstream dependencies some of which aren't under your control and can't be changed. Sounds fun.

This isn't true. For structs you can use 'this = ...' to overwrite yourself (including readonly fields) and reflection lets you set them too.

fwiw those are both gross but I've run into both in production code (not written by me, naturally)

The same can be said for setters and getters with a backing field, you can access them through reflection. I can't remember how it works for properties with implicit backing fields but I thought they could be set via reflection as well?

You can find the backing field and set it, yes, but the name is at least not predictable because the compiler mangles it (which discourages doing this because getting a grip on the field is harder)