Which is better between a readonly modifier and a private setter?

Question

I\'ve been working on creating a class and suddenly a thought came to my mind of what is the difference between the two codes:

public readonly string Product         


        

Answer 1

The first is a field whose value can be set only at instantiation.

The second is a property whose value can be set at any time (but only by its containing object).

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Correction: The property can be set at any time by any instance of the same class (and not only by its containing object).