Re: [boost] low-level sub-allocation/alignment challenge

From: Darin Adler (darin_at_[hidden])
Date: 2000-08-24 12:40:47

on 8/24/00 10:17 AM, Greg Colvin at greg_at_[hidden] wrote:

> So this is a POD too?
> 
>   struct Rule
>   {
>       unsigned long cost;
>       const void* action;
>       char& operator[](size_t i) { return ((char*)(&action+1))[i]; }
>       char operator[](size_t i) const { return ((char*)(&action+1))[i]; }
>   };

Yes. I went and reviewed the rules on POD in the standard.

A POD type is (3.9/10) one of:

    a) a scalar type
    b) a POD-struct type
    c) a POD-union type
    d) an array with elements of POD type
    e) a cv-qualified POD type

A POD-struct (9/4):

    1) is an aggregate class
    2) has no non-static data members that are
        a) pointer to member
        b) non-POD-struct
        c) non-POD-union
        d) arrays of non-POD-struct
        e) arrays of non-POD-union
        f) reference
    3) has no user-defined copy assignment operator
    4) has no user-defined destructor

An aggregate class (8.5.1):

    1) has no user-declared constructors
    2) has no private or protected non-static data members
    3) has no base classes
    4) has no virtual functions

Your example fits the bill!

    -- Darin