typedef vs. class definition

[jsanga]

What are the major benifits / drawbacks to the following code?

myheader.h

#include <vector>
struct MyStruct {
int f1;
float f2;
...
};

typedef std::vector< MyStruct > STRUCTURES;
class STRUCTURES_TOO : public std::vector< MyStruct > {};

The reason for asking is; I'm trying to reduce header file includes,
improve compile time and write better conforming code. The issue here
is when other classes need to pass around STRUCTURES as a parameter, I
am forced to include "myheader.h" for the definition.

anotherheader.h
#inlcude "myheader.h"
class MyClass {
public:
DoSomething( const STRUCTURES &s ); // require myheader.h
};

However, by declaring STRUCTURES_TOO I am able to do the following

anotherheader.h

class STRUCTURES_TOO; // Just forward ref the class
class MyClass {
public:
DoSomething( const STRUCTURES_TOO &s );
};

I know the STL doesn't have virtual destructors, so derrived classes
are frowned upon. But in this case I don't have the problem of passing
around base classes.

 

[Jonathan Mcdougall]

What are the major benifits / drawbacks to the following code?

These are not equivalent. You cannot and should not try to replace one
by the other, it makes no sense.

myheader.h

#include <vector>
struct MyStruct {
int f1;
float f2;
...
};

typedef std::vector< MyStruct > STRUCTURES;
class STRUCTURES_TOO : public std::vector< MyStruct > {};

The reason for asking is; I'm trying to reduce header file includes,
improve compile time and write better conforming code. The issue here
is when other classes need to pass around STRUCTURES as a parameter, I
am forced to include "myheader.h" for the definition.

Separate the typedef from the class definition.

anotherheader.h
#inlcude "myheader.h"
class MyClass {
public:
DoSomething( const STRUCTURES &s ); // require myheader.h
};

No, it requires the typedef and the typedef only requires a declaration
of the class.

However, by declaring STRUCTURES_TOO I am able to do the following

anotherheader.h

class STRUCTURES_TOO; // Just forward ref the class
class MyClass {
public:
DoSomething( const STRUCTURES_TOO &s );
};

You're using inheritance not because it suits your design, but because
you want to reduce compiling time. That's a bad choice, imho, and it's
worst because there are other ways.

I know the STL doesn't have virtual destructors, so derrived classes
are frowned upon.

Not if it suits your design.

But in this case I don't have the problem of passing
around base classes.

Jonathan