Question

Say I have a class with some properties and some methods for manipulating those properties:

public class PersonModel
{
    public string Name { get; set; }
    public string PrimaryPhoneNumber { get; set; }

    public void LoadAccountInfo(AccountInfo accountInfo)
    {
        this.Name = accountInfo.Name;
    }

    public void LoadPhoneInfo(PhoneInfo phoneInfo)
    {
        this.PrimaryPhoneNumber = phoneInfo.PhoneNumber;
    }
}

Typical usage would be:

var model = new PersonModel();
model.LoadAccountInfo(accountInfo);
model.LoadPhoneInfo(phoneInfo);

I think it would be cool to make the methods chainable:

    public PersonModel LoadAccountInfo(AccountInfo accountInfo)
    {
        this.Name = accountInfo.Name;
        return this;
    }

    public PersonModel LoadPhoneInfo(PhoneInfo phoneInfo)
    {
        this.PrimaryPhoneNumber = phoneInfo.PhoneNumber;
        return this;
    }

Then usage would be:

var model = new PersonModel()
    .LoadAccountInfo(accountInfo)
    .LoadPhoneInfo(phoneInfo);

But I am not returning a modified “clone” of the passed-in PersonModel object in each of these chainable methods. They are just modifying the original object and returning it (for convenience). To me, this creates an ambiguity because someone calling these methods may assume that they are immutable (i.e. they leave the original object intact but return a modified object).

Does that violate any sort of best practice regarding fluent/chainable interfaces?

Answer 1

Personally I think that immutability and fluent interfaces are separate concerns. It may be that you find immutability in general to be a good thing, a best practice. But this would be whether or not you used a fluent interface.