How to understand primitive types are immutable
How to understand primitive types are immutable
Primitive type
Primitive types such as int, long, bool, string, etc. are basic types provided by C# language. We can create new class or struct based on these native types. They are the core fields that can carry information.
Mutable type
Imagine that one man whose original name is Bruce, but now he wants to change his name to Dick. Well, after changing his name, is the man who has a new name now still the one before? Of course, the answer is YES. One property of his was just changed, but that doesn't mean the man was not the man. Just like we are getting older. Does that mean me of today is not that me of yesterday? No. What I am speaking is about the mutable type. Every comprehensive system is always mutable. It's changing itself apart from its nature. In programming world, one class instance can make some changes inside itself, but the pointer to that instance keeps same.
Immutable type
As just mentioned, if some kind of changes happen and the nature of that thing changes as well, we can say a new thing appears, which means the new one is not the old, just like chick comes out from egg. Number 1 is not 2. String "hello" is not "world". Boolean true is not false. We are not able to modify the content of value 1 because 1 per se is primitive. There is nothing inside the 1. Even if we can change something, that will make 1 not 1 any more. The most classical is string type. One string value is composed of some characters. Its value like "good" is unchangeable. We are always creating new values if we want to change it on C# side.
Type can be designed as immutable
In fact, string is designed to be immutable as well as DateTime, Guid, Regex, etc. We are allowed to create such immutable types so that caller has to create new instances all the time for security purpose such as thread safety, reliability or some reasons else. Any change attempt to the object will fail.
Variable and data (value)
Variable is created to store data. The data can be value of Value Type or Reference Type instance. For Value Type, variable holds all the information of that instance. For Reference Type, variable just holds the reference (i.e. pointer). The content of variable is always changeable unless the variable is readonly or constant. So, mutable variable is different from mutable type. They are two matters.
