const behaviour

[Timon Gehr]

On 06/22/2012 11:21 AM, Namespace wrote:
> Based to the current const discussions (once again) I wanted to appease
> my curiosity and want to ask why the following code works as described
> in the comments:
>
> [code]
>
> import std.stdio;
>
> class Bar { }
>
> class Foo {
> private:
>      string _text;
>
>      Bar _b;
>
> public:
>      this(string text, Bar b) {
>          this._text = text;
>          this._b = b;
>      }
>
>      // const_behaviour.d(18): Error: cannot implicitly convert
> expression (this._b) of type const(Bar) to const_behaviour.Bar
>      Bar GetB() const pure nothrow { /// <- must be const(Bar) instead
> of Bar
>          return this._b;
>      }
>
>      string GetText() const pure nothrow { /// <- no const(string) is
> neccessary. Why?
>          return this._text;
>      }
> }
>
> void main() {
>      Bar b = new Bar();
>
>      Foo f = new Foo("foobar", b);
> }
>
> [/code]

string is immutable(char)[] and const(immutable(char)[]) implicitly
converts to immutable(char)[]. Or put differently, a string doesn't
have to be const-qualified because it cannot be changed anyway.