Try it with dynamic values and see what happens. Then you can answer your own question.

public long TimeStamp1 { get; } = DateTime.Now.Ticks;
public long TimeStamp2 => DateTime.Now.Ticks;

Console.Log(Foo.TimeStamp1);
Console.Log(Foo.TimeStamp2);
Thread.Sleep(3000);
Console.Log(Foo.TimeStamp1);
Console.Log(Foo.TimeStamp2);
Thread.Sleep(3000);
Console.Log(Foo.TimeStamp1);
Console.Log(Foo.TimeStamp2);

My personal suspicion is that ReSharper thinks most people meant to have dynamic resolution of the property getter. ReSharper would then expect people to be surprised to discover that the initial value is never changed. (I can submit this as an answer if that's useful.)

I think Michael is right. Getters are just syntactical sugar that get transformed into parameterless functions. In most cases the caller expects for this to evaluate based on object's state and not "cache" the initial value.

If you want to store the initial evaluation result, define a static readonly field instead to better convey the meaning (it is not supposed to change).

Pretty sure OP's understanding is correct. { get; } = 1 + 2; will compute once with the value stored in a hidden backing field. (For a non-static class/property it would be computed once for each instance).

=> 1 + 2; will evaluate each time (possibly save for optimizations).

What I wonder though is why Rider is suggesting this. If I write this code I have no such suggestion. There is a refactoring available to convert it to the arrow style, but it is specifically labelled "To computed property (evaluate each read)".

If Rider really is suggesting this it may be that you have set somewhere a preference for the arrow style; but I'm not sure about that. I think it may be that your real example differs in an important way and that is why the suggestion is being made, but that's just a guess.

Michael‭ I don't care about performance per se, but about understanding the language. I should have worded my question differently. Confirmation that a get-only property and a calculated property are different answers my question. Many thanks!

Actually, Rider does not always suggest the simplification. I was wrong about that. Probably it only suggests the change when the value is a static struct such as an int or a bool.

I would accept either Michael‭'s or Dave‭'s comments as answers.