about the new const regime

[davidl]

在 Wed, 02 Jan 2008 01:14:22 +0800，Daniel919 <Daniel919 at web.de> 写道:

> (dmd 2.009)
>
> What's the difference between "const T" and "invariant T", if T is a  
> value type (builtin type or struct)?
>
> Value types are always a copy and never refer to anything.
> So a const(T) can't be changed.
>
> Example:
> typeid(string) == "invariant(char)[]" (default)
>
> string s = "bla";
> s[0] = 'x'; //Error, cannot change a invariant(char)
> But then, where is the difference to const(char)?
>
The difference is :

string s = "bla";
s = "abc"; 	// compile, you can reassign to an invariant array with  
another invariant array, but you can't change it partially.
s[0] = 'x'; //error as you said




> If there really is no difference, shouldn't string be "const(char)[]"  
> then? And maybe invariant(T) should be an error, when T is a valuetype?
>
>
> About enum:
> Instead of the current "abuse" of enum to also define values that take  
> no space, I would like a new keyword, which can be used more general:
>
> meta
>
> metaprogramming <=> compile time programming
> meta <=> compile time
>
> meta x = 1; <=> meta int x = 1;
> x is a compile time value of type int.
>
> enum { red, green, blue } //<=>
> meta red = 0, green = 1, blue = 2;
>
>
> This could also help to make a better distinction:
> class Foo { static int x; }
> means x is not bound to an object. using static this(), x can be  
> assigned at runtime
>
> static if( ... ) ...
> means evaluate the if at compile time
>
> With the new keyword, it could be renamed to
> meta if( ... ) ...
>
> static <=> not bound to an object
> meta <=> compile time
>
>
> Best regards and happy new year,
> Daniel



-- 
使用 Opera 革命性的电子邮件客户程序: http://www.opera.com/mail/