C++Talk.NET

mlepage · Guest

I have some code that has a global two dimensional array of structs
with member variables, used like this:

array[i][j].member = 42;

Consider the following series of changes:

1) Global array becomes global object with operator[] overloaded to
return a second object initialized with argument i.

2) That second object has operator[] overloaded to return a third
object initialized with arguments i and j.

3) That third object has function member() which returns a fourth
object initialized with arguments i and j, and a code for member.

4) That fourth object has operator= overloaded to take arguments i, j,
the code for member, and the int argument, and go off in a database to
set the appropriate value using that information.

So basically, the big global array of structs is replaced by a bunch
of magic to store it all in a database instead. Temporary value
objects do the work. Here's the code:

struct GlobalObject
{
SecondObject operator[](int n1) { return SecondObject(n1); }
};

struct SecondObject
{
SecondObject(int n1) : m_n1(n1) {}
ThirdObject operator[](int n1) { return ThirdObject(m_n1, n2); }
const int m_n1;
};

struct ThirdObject
{
ThirdObject(int n1, n2) : m_n1(n1), m_n2(n2) {}
FourthObject member() { return FourthObject(m_n1, m_n2,
MEMBER_CODE); }
const int m_n1;
const int m_n2;
};

struct FourthObject
{
FourthObject(int n1, int n2, int n3) : m_n1(n1), m_n2(n2),
m_n3(n3) {}
FourthObject& operator=(int n)
{
// use all this info to set something in a database to n
return *this;
}
const int m_n1;
const int m_n2;
const int m_n3;
};

The global object is now declared like this:

GlobalObject array;

So now the use is like this (only a minor difference in syntax):

array[i][j].member() = 42;

I've tested this and it seems to work as expected.

My question is, are there any problems with this approach? Will the
temporaries live long enough to ensure that the assignment (which does
work in a database) is using valid data?

(I think it is, but I want to double check, since my application has
some weird errors that puzzle me. I want to ensure that this approach
is valid before I rule it out as a possible cause.)

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Ben Hutchings · Guest

mlepage wrote:

Maxim Yegorushkin · Guest

mlepage <antimeta (AT) gmail (DOT) com> wrote: