• Kevin Bealer <Kevin_member pathlink.com> May 11 2004
• James McComb <alan jamesmccomb.id.au> May 11 2004
• J Anderson <REMOVEanderson badmama.com.au> May 11 2004

Kevin Bealer <Kevin_member pathlink.com> writes:

I was thinking about "const" and I realized: D already has a form of const.
"The absence of a write method means that the property is read-only."

class const_foo {
char[] msg; /+ mutable member +/
int key() { return m_key; }

private:
int m_key;
};

/+ non-const foo +/
class foo : const_foo {
int key(int k) { m_key = k };
};

Now, functions that take a const_foo will not have access to key.  For those who
are about to say "this violates IS-a": Just imagine the adjective had the
opposite meaning; instead of "const foo" and "foo", think "readable foo" and
"readable writeable foo".

Kevin

James McComb <alan jamesmccomb.id.au> writes:

Kevin Bealer wrote:

 Now, functions that take a const_foo will not have access to key.  For those
who
 are about to say "this violates IS-a": Just imagine the adjective had the
 opposite meaning; instead of "const foo" and "foo", think "readable foo" and
 "readable writeable foo".


I think you mean "writeable readable foo". :)

I "writeable readable foo" IS A "readable foo".

James McComb

J Anderson <REMOVEanderson badmama.com.au> writes:

Kevin Bealer wrote:

I was thinking about "const" and I realized: D already has a form of const.
"The absence of a write method means that the property is read-only."

class const_foo {
char[] msg; /+ mutable member +/
int key() { return m_key; }

private:
int m_key;
};

/+ non-const foo +/
class foo : const_foo {
int key(int k) { m_key = k };
};

Now, functions that take a const_foo will not have access to key.  For those who
are about to say "this violates IS-a": Just imagine the adjective had the
opposite meaning; instead of "const foo" and "foo", think "readable foo" and
"readable writeable foo".

Kevin



  



//common module 1
template ConstT(T) //This would be in another module
{
  struct Const
  {
      private int val;
           static Const opCall(T val)
      {
          Const t;
          t.value = val;
          return t;
      }

      int value() { return val; }
  }
}

alias ConstT!(int).Const const;

//module 2

void test(const value)
{
  int x = value.value;

//You just can't change the variable (well at least not without force).

}

void main()
{
  int a;
  test(const(a)); //Ok there's a small bit of extra typing -> if D only 
had automatic boxing....
}

-- 
-Anderson: http://badmama.com.au/~anderson/