Property with private setter versus get-only-property

Question

C# 6.0 introduces the ability to define get-only properties:

public ICommand AddCommand { get; } 

Now when defining another property like the following, ReSharper suggests Auto-property can be made get-only:

private List<Screenshot> Screenshots { get; set; } 

Futhermore, ReSharper doesn't say a thing when defining private getters:

public ICommand AddCommand { get; private set; } 

What's the difference between a public get-only property (such as the first AddCommand), a private get-only property (such as the Screenshots property) and the public private setter property (such as the second AddCommand)?

My WPF application doesn't seem to care whether its public property (UICommand) contains a private setter or no setter at all, but surely there must be a difference?

Answer 1

Short answer:

public ICommand AddCommand { get; } 

will be backed by a readonly field and no C# code will be able to change it beyond the execution of the constructors.

Also, the compiler will generate code to directly assign the backing filed, as there is no property accessor.

On the other hand:

public ICommand AddCommand { get; private set; } 

will be backed by a non-readonly field and can be assigned at any time by any code with access to private members.

In this case, the compiler will generate normal property setting code.

To the outside world, a private setter is as if it doesn't exist. So, it's the same as if it didn't really exist.