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dima
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 Posted: Thu Oct 23, 2003 3:45 pm Post subject: how to change f(t&) to f(t*) and not recode the function |
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I have something like this:
typedef std::map<std::string,T> MAP_TYPE;
void f(POSITION_MAP_TYPE::mapped_type t){
t.do();
}
now, i want to see if i can gain any performance by redefining my map
like so:
typedef std::map<std::string,T*> MAP_TYPE;
if i don't like it, i want to switch back.
my goal: not have to recode all function signatures and all code from
t.do()
to t->do() back and forth.
is there way to achive this? On a side note: I can do something like
typedef typename MAP_TYPE::pointer ptr; but i have not figured out how
to use it. In fact, i don't know how to use these
typedefs(pointer,reference etc) that containers define, if anybody can
show an example would be great.
thanks.
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Michael Tiomkin
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| Posted: Fri Oct 24, 2003 3:26 pm Post subject: Re: how to change f(t&) to f(t*) and not recode the function |
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[email]dbabits (AT) hotmail (DOT) com[/email] (dima) wrote in message news:<5c72b580.0310222006.121e8538 (AT) posting (DOT) google.com>...
| Quote: | I have something like this:
typedef std::map<std::string,T> MAP_TYPE;
void f(POSITION_MAP_TYPE::mapped_type t){
t.do();
}
now, i want to see if i can gain any performance by redefining my map
like so:
typedef std::map<std::string,T*> MAP_TYPE;
|
For every large type T you'll probably get huge performance benefits.
STL containers copy their data, and using pointers will make
adding/finding/deleting an item much faster. However,
you'll need a different memory management scheme
for containers of pointers. For example, you wouldn't like
to delete an object after adding a ptr to it to the map.
A good compromise could be using a ptr with refcount.
An object will contain only two words, and its copy constructor
and destructor will be relatively simple.
| Quote: | if i don't like it, i want to switch back.
|
It wouldn't be very easy because of the different memory management.
You'll have to change your USE of the map.
| Quote: | my goal: not have to recode all function signatures and all code from
t.do()
to t->do() back and forth.
|
You can use a map to T& instead of T*.
Most compilers would use a ptr as implementation of reference
anyway.
| Quote: | is there way to achive this? On a side note: I can do something like
typedef typename MAP_TYPE::pointer ptr; but i have not figured out how
to use it. In fact, i don't know how to use these
typedefs(pointer,reference etc) that containers define, if anybody can
show an example would be great.
|
It's better to read a good C++ book. Look at the FAQ to see the references
to these books. I'm not sure you really need any typedefs from STL
containers beside the iterators.
Michael
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David Turner
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| Posted: Fri Oct 24, 2003 7:22 pm Post subject: Re: how to change f(t&) to f(t*) and not recode the function |
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"dima" <dbabits (AT) hotmail (DOT) com> wrote
| Quote: | I have something like this:
typedef std::map<std::string,T> MAP_TYPE;
void f(POSITION_MAP_TYPE::mapped_type t){
t.do();
}
now, i want to see if i can gain any performance by redefining my map
like so:
typedef std::map<std::string,T*> MAP_TYPE;
if i don't like it, i want to switch back.
my goal: not have to recode all function signatures and all code from
t.do()
to t->do() back and forth.
|
You could try something like this:
template<typename T>
struct HereAndThere
{
T* operator ->() { return static_cast<T*>(this); }
const T* operator ->() const { return static_cast<const T*>(this); }
};
class MyType: public HereAndThere<MyType>
{
// etc
};
typedef std::map<std::string, MyType> ContainerMap;
typedef std::map<std::string, MyType*> ReferenceMap;
int main()
{
ContainerMap a;
ReferenceMap b;
a["Test"] = MyType();
b["Test"] = new MyType();
ContainerMap::iterator i = a.find("Test");
ReferenceMap::iterator j = b.find("Test");
(*i)->foo();
(*j)->foo();
return 0;
}
Regards
David Turner
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Ulrich Eckhardt
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| Posted: Fri Oct 24, 2003 7:29 pm Post subject: Re: how to change f(t&) to f(t*) and not recode the function |
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dima wrote:
| Quote: | typedef std::map<std::string,T> MAP_TYPE;
void f(POSITION_MAP_TYPE::mapped_type t){
t.do();
}
now, i want to see if i can gain any performance by redefining my map
like so:
typedef std::map<std::string,T*> MAP_TYPE;
if i don't like it, i want to switch back.
my goal: not have to recode all function signatures and all code from
t.do()
to t->do() back and forth.
|
You could code a set of inline forwarding functions that are overloads orf
the existing ones.
In addition to
void f(T& t);//def'd elsewhere
you add another
inline void f(T* t)
{ return f(*t); }
or vice versa.
Uli
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dima
Guest
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| Posted: Sat Oct 25, 2003 8:40 am Post subject: Re: how to change f(t&) to f(t*) and not recode the function |
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"David Turner" <david (AT) firepro (DOT) co.za> wrote
| Quote: | "dima" <dbabits (AT) hotmail (DOT) com> wrote in message
news:5c72b580.0310222006.121e8538 (AT) posting (DOT) google.com...
I have something like this:
typedef std::map<std::string,T> MAP_TYPE;
void f(POSITION_MAP_TYPE::mapped_type t){
t.do();
}
now, i want to see if i can gain any performance by redefining my map
like so:
typedef std::map<std::string,T*> MAP_TYPE;
if i don't like it, i want to switch back.
my goal: not have to recode all function signatures and all code from
t.do()
to t->do() back and forth.
You could try something like this:
template<typename T
struct HereAndThere
{
T* operator ->() { return static_cast<T*>(this); }
const T* operator ->() const { return static_cast<const T*>(this); }
};
class MyType: public HereAndThere<MyType
{
// etc
};
typedef std::map
typedef std::map<std::string, MyType*> ReferenceMap;
int main()
{
ContainerMap a;
ReferenceMap b;
a["Test"] = MyType();
b["Test"] = new MyType();
ContainerMap::iterator i = a.find("Test");
ReferenceMap::iterator j = b.find("Test");
(*i)->foo();
(*j)->foo();
return 0;
}
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thanks David, this is a very nice idea, except you have to call
i->second->foo()
Here's what i came up with in the mean time, critisism welcome:
template<class T> inline T* ptr(T& v) { return &v;}
template<class T> inline const T* ptr(const T& v){ return &v;}
template<class T> inline T* ptr( T* v){ return v; }
template<class T> inline const T* ptr(const T* v){ return v; }
template<class T> inline boost::shared_ptr<T>& ptr(shared_ptr<T>&
v){return v;}
template<class T> inline const boost::shared_ptr<T>& ptr(const
shared_ptr<T>& v){return v;}
template<class T> inline T& ref( T& v){ return v; }
template<class T> inline const T& ref(const T& v){ return v; }
template<class T> inline T& ref( T* v){ assert(v);return
*v;}
template<class T> inline const T& ref(const T* v){ assert(v);return
*v;}
template<class T> inline T& ref( boost::shared_ptr<T>&
v){return *v;}
template<class T> inline const T& ref(const boost::shared_ptr<T>&
v){return *v;}
And an example of usage:
void test_ptr(){
Foo* pe=new Foo;
Foo e;
boost::shared_ptr<Foo> sm(new Foo);
ptr<Foo>(pe)->fn();
ptr(e)->fn();
ptr<Foo>(sm)->fn();
ref<Foo>(pe).fn();
ref<Foo>(e).fn();
ref<Foo>(sm).fn();
}
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