Re: [Boost-users] Macro to contruct/allocate a shared_ptr?

14 Jul 2006

      On 7/14/06, Michael Nicolella  wrote:
...
What's wrong with
boost::shared_ptr<Test> test( new Test );
boost::shared_ptr<Test> test( new Test( 100, 'a', "hello" ) );
http://boost.org/libs/smart_ptr/shared_ptr.htm
I'm not sure how NEW0 or NEW or New is better than new... Making a macro
that calls new doesn't encapsulate the call to new, it only obscures it and
makes it less flexible.
-----Original Message-----
From: bringiton bringiton [mailto:kneeride@gmail.com]
Sent: Thursday, July 13, 2006 6:38 PM
To: boost-users@lists.boost.org
Subject: [Boost-users] Macro to contruct/allocate a shared_ptr?
I'm trying to define a MACRO that creates a shared_ptr and hides memory
allocation. Here is what i have so far:
#define NEW0(T) boost::shared_ptr<T>(new T()); #define NEW1(T, p1)
boost::shared_ptr<T>(new T(p1)); #define NEW2(T, p1, p2)
boost::shared_ptr<T>(new T(p1, p2)); #define NEW3(T, p1, p2, p3)
boost::shared_ptr<T>(new T(p1, p2, p3));
---------------------------------
Example of usage for the type Test:
class Test {
public:
       Test() {;}
       Test(int p1) {;}
       Test(int p1, char p2) {;}
       Test(int p1, char p2, std::string p3) {;} };
boost::shared_ptr<Test> p0 = NEW0(Test); boost::shared_ptr<Test> p1 =
NEW1(Test, 100); boost::shared_ptr<Test> p2 = NEW2(Test, 100, 'a');
boost::shared_ptr<Test> p3 = NEW3(Test, 100, 'a', "hello");
---------------------------------
Is there a better way to do this? I would prefer to use a function instead
of a MACRO. But I don't think it is possible because it is not know how many
paramaters are in T's constructor.
// not sure how to do this (or whether possible) // i am not sure how to
implement the variable parameters // (hense the .. in my syntax) template
<class T> boost::shared_ptr<T> New(...) {
       boost::shared_ptr<T> p(new T(...));
       return p;
}
Any ideas? I often have problems with the c++ syntax when creating my own
containers because i want to allocate T within the implementation (instead
of passing pointers and having the user manage the memory).
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I just have a problem with having the user manage the memory. ie I'd
rather do the following:

shared_ptr<Test> p(1, 'a', "hello");
or:
shared_ptr<Test> p = newptr<Test>(1, 'a', "hello");

instead of:

shared_ptr<Test> p(new p(1, 'a', "hello"));

but i guess that's a limitation of the language. to get around this i
do the following:

class Test {
private:
   Test(int p1, char p2, string p3) {;}
public:
   static shared_ptr<Test> NewTest(int p1, char p2, string p3) {
      return p(new Test(p1, p2, p3);
   }
...

// memory allocation hidden
shared_ptr<Test> t = Test::NewTest(1, 'a', "hello");

but this is a hassle. esp when many constructors...