Re: [boost] Proposal: statefull objects

From: Peter Dimov (pdimov_at_[hidden])
Date: 2001-07-20 07:24:25

From: "Fernando Cacciola" <fcacciola_at_[hidden]>
> In order to introduce this proposal let's consider the following
situations:
>
> CASE A:
> =======
>
> struct image
> {
>   ...
>   int get_pixel( int x, int y) const ;
>   ...
> } ;
>
> How should we deal with the case of x,y being outside the image?

A function should not try to do too many things.

bool is_inside(int x, int y) const;
color_type get_pixel(int x, int y) const;

[Other cases that demonstrate the point better snipped.]

> I'd like to know your opinions.

This is a discriminated union, like 'any'. The only difference is that 'any'
accepts any type + void, while your proposed class accepts only T or void.

People that program in discriminated-union-capable languages would like your
proposal. :-) Do you think that optional<T> would be a better name?

--
Peter Dimov
Multi Media Ltd.