Re: [boost] range idea (single)

From: Simon Buchan (simon_at_[hidden])
Date: 2005-10-27 01:02:20

Joe Gottman wrote:
> "Neal Becker" <ndbecker2_at_[hidden]> wrote in message 
> news:djogoc$u8q$1_at_sea.gmane.org...
>> Suppose one adopts the range concept.  All algorithms are written to 
>> accept
>> ranges as arguments.
>>
>> It is common to want to implement a function F, which operates on one data
>> element.  For example:
>>
>> template<typename T>
>> T sqr (T x) { return x * x; }
>>
>> Also, implement a version that operates on a container.  This could be 
>> done
>> by defining only the single element version, and a version of transform,
>> that operates on ranges.
>>
>> Here's an interesting idea.  Suppose instead that only the range version 
>> of
>> F is defined, but a range type is made that encapsulates a single element.
>> Again, only 1 version of F needs to be defined.
>>
>> Here is an outline:
>> template<typename T>
>> struct Single {
>>  typedef T* iterator;
>>  typedef const T* const_iterator;
>>  typedef size_t size_type;
>>  Single (T& _x) : x (_x) {}
>>  T& x;
>>  size_t size() const { return 1; }
>>  iterator begin() { return &x; }
>>  const_iterator begin() const { return &x; }
>>  iterator end() { return &x+1; }
>>  const_iterator end() const { return &x+1; }
>> // not complete yet...
>> };
>>
> 
> The one thing I'd be concerned about is slicing.
> struct Base {};
> struct Derived : public Base {int x; }; // Note that Derived does have data 
> members.;
> 
> Derived d;
> Single<Base> foo(d);
> 
> Under these circumstances, does calling foo.end(), which will return an 
> address in the middle of d, cause any problems?
> 
> Joe Gottman 

What happens in std:: containers?

        vector<Derived> vd;
        vector<Base>::iterator = vd.begin();

Compile error!

-- 
don't quote this