When should use Readonly and Get only properties

Question

In a .NET application when should I use \"ReadOnly\" properties and when should I use just \"Get\". What is the difference between these two.

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Answer 1

readonly properties are used to create a fail-safe code. i really like the Encapsulation posts series of Mark Seemann about properties and backing fields:

http://blog.ploeh.dk/2011/05/24/PokayokeDesignFromSmellToFragrance.aspx

taken from Mark's example:

public class Fragrance : IFragrance
{
    private readonly string name;

    public Fragrance(string name)
    {
        if (name == null)
        {
            throw new ArgumentNullException("name");
        }

        this.name = name;
    }

    public string Spread()
    {
        return this.name;
    }
}

in this example you use the readonly name field to make sure the class invariant is always valid. in this case the class composer wanted to make sure the name field is set only once (immutable) and is always present.