Can someone explain why i can change this immutable variable please?

[Orvid King]

On Wednesday, 9 October 2013 at 15:26:35 UTC, Gary Willoughby 
wrote:
> Can someone explain why i can change Bar's immutable name 
> member please?
>
> 	import std.stdio;
>
> 	class Foo
> 	{
> 		public void change(string name)
> 		{
> 			name = "tess";
> 			writeln(name);
> 		}
> 	}
>
> 	class Bar
> 	{
> 		private static immutable string name = "gary";
>
> 		public void test()
> 		{
> 			auto foo = new Foo();
> 			foo.change(this.name);
> 		}
> 	}
>
> 	void main(string[] args)
> 	{
> 		auto bar = new Bar();
> 		bar.test();
> 	}
>
> I thought an error would inform me that the `Foo.change` 
> function is being called with the wrong parameter type.

This would fail if you were to declare `change` as `void 
change(ref string name)`. This is valid because you are passing 
the value of a reference to a string. `Bar.name` is an immutable 
reference to a string, but your only passing a copy of that 
reference to `Foo.change`, that copy is mutable by default.