Re: [boost] the best possible c++ properties (implementation).

Subject: Re: [boost] the best possible c++ properties (implementation).
From: Christopher Jefferson (chris_at_[hidden])
Date: 2010-03-01 15:10:00

On 1 Mar 2010, at 20:03, Daniel Larimer wrote:

> On Mar 1, 2010, at 2:48 PM, Zachary Turner wrote:
> 
>> 
>> 
>> On Mar 1, 2010, at 1:39 PM, Christopher Jefferson <chris_at_[hidden]> wrote:
>> 
>>> 
>>> On 1 Mar 2010, at 18:24, Germán Diago wrote:
>>> 
>>>> for trivial properties it's the same. But maybe in the future
>>>> properties will be extended with some metadata.
>>>> anyway, for trivial properties it's the same.
>>> 
>>> I don't understand what your library does. Having your most simple example say it does nothing at all is not helpful!
> 
> Where properties are useful is eliminating the need to define "setters/getters" while ensuring that
> no one ever gets a direct reference to the actual data.  This is critical for multi-threaded programs where
> you want to reduce "shared state".     
> 
> My issue with the approach is that it drastically increases the size of your object and the cost of calling constructors. 
> 
> Presumably each "int" now has 2 member function pointers.   Thus 4 bytes becomes 20 bytes (best case, 64 bit ptrs) and more on
> compilers that have bigger member function pointers.

What exactly do you mean?

struct X
{ int i; };

class X
{
  int i;
  public:
  int geti() { return i; }
  void seti(int _i) { i = _i;}
};

Are both the same size (sizeof(int)). Further, on any reasonable compiler geti, seti and in fact X itself will be totally optimised away, leaving just the same code as if we had used a raw int.

Chris