Effect of declaring a class immutable ?

[Basile B. via Digitalmars-d-learn]

On Thursday, 26 May 2016 at 14:12:23 UTC, chmike wrote:
> I couldn't find any information about this on the dlang web 
> site.
>
> What is the effect adding the immutable attribute to a class 
> like this
>
> immutable class MyClass { ... }
>
> The compiler doesn't complain.
> Will it add the immutable attribute to all members ?

Since immutable is transitive everything in your class will be. 
So basically the only thing you can do is

- create a new immutable(MyClass)
- sets the instances variables in the ctor.
- calls the method (which can't do anything on the variables).

And that's all, e.g:

----
immutable class Foo
{
     int i;
     this(int i){this.i = i;}
     void method(){}
}

void main()
{
     immutable(Foo) foo = new immutable(Foo)(1);
     //foo.i = 8; // not possible since i is immutable
     Foo foo1 = cast(Foo) foo; // cast away immutable from the 
type.
     //foo1.method; // not pissible since method is immutable
}
----

So it's more or less useless, unless you want to wrap some 
variables in a class to simplify completion in the IDE or 
whatever other reasons.

_________________

By the way the doc for "immutable class Stuff" is here: 
https://dlang.org/spec/const3.html#immutable_type, it's a type 
constructor. "immutable" is fully part of the type.