I can define a class like below:
public class MyClass
{
public int Id { get; }
public MyClass(int id) => Id = id;
}
And I have to define the Id from the constructor and it will be read-only.
But if I want to use Init only setters in the C# 9.0, what does it and how can I use it?
public class MyClass
{
public int Id { get; init; }
}
In a nutshell:
var obj = new MyClass
{
Id = 42 // totally fine
};
obj.Id = 43; // not OK, we're not initializing
Trivial in this case and not much different to using a constructor parameter, but useful in some more complex scenarios where you don't want 200 constructor parameters, but you do want it to be outwardly immutable once constructed.
Init only setters provide consistent syntax to initialize members of an object. Property initializers make it clear which value is setting which property. The downside is that those properties must be settable.
With that, you don't need to provide the value at the beginning and the constructor and you can do it afterward:
var myClass = new MyClass
{
Id = 10
}
and it will be sealed and you cannot change it anymore.
myClass.Id = 43; // not allowed
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