Two question about array

[Derek Parnell]

On Sun, 30 Dec 2007 09:09:37 -0500, Alex wrote:

> 1. Is array a class derived from Object? If yes, why i get error message with the following code:
> 	int[] array;
> 	Object obj = array;

No, an array is not a class.

> If not, is there any general type can represent either an Integer, or an Array? Or a character string?

Have a look at the std.boxer module, that might be what you are looking
for. 

> 2. simpleArray.length = simpleArray.length * 2 can pass the compile but simpleArray.length *= 2 can't. The compiler complains "simpleArray.length is not an lvalue", what's the problem?

This is a current restriction in D.

The reason is that the .length is a property (albeit a built-in one) and
properties are implemented as function calls. This means that ...

    simpleArray.length *= 2

is equivalent to ...

    get_length(simpleArray) *= 2

which as you can imagine is not going to do what you want. Whereas ...

   simpleArray.length = simpleArray.length * 2

is equivalent to ...

   set_length(simpleArray, get_length(simpleArray) * 2 )

Hopefully, this is one of the restrictions that can be removed soon.

This restriction applies to user defined properties too.

For example:

class Foo
{
    float m_Value  = 0;

    int  val()       { return cast(int)m_Value; }
    void val( int x) { m_Value = cast(float)x); }
}

 Foo f = new Foo;

 int a;

 a = f.val; // okay
 a += 2;
 f.val = a; // okay;

 f.val += 2; // Not okay.


 

  


-- 
Derek Parnell
Melbourne, Australia
skype: derek.j.parnell