指针容器上的std :: for_each

Question

In some class I have a hash_set of pointers:

std::hash_set<GameObject*> gameObjects;

I wish to iterate through all of them and call update. With iterators this would be like this:

for(std::hash_set<GameObject*>::iterator it = gameObjects.begin(), it_end = gameObjects.end(); it != it_end; ++it)
{
(*it)->update();
}

This is too much code; I want to use std::for_each .

If I had just hash_set<GameObject> , this would look like this:

std::for_each(gameObjects.begin(), gameObjects.end(), std::mem_fun_ref(&GameObject::update));

or, if update was expecting a parameter,

std::for_each(gameObjects.begin(), gameObject.end(), std::bind2nd(std::mem_fun_ref(&GameObject::update), deltaTime));

How would these both expressions look for the hash_set of pointers?

I am using MS VisualStudio 2010.

Answer 1

If you have a compiler which supports lambdas (C++11), you could use

std::for_each(gameObjects.begin(), gameObjects.end(), [=](GameObject* o) {o->update(deltaTime);});

Using lambdas is a good option for many STL algorithms, but, as @phresnel points out, the range-based for loop (also C++11) is more concise in this case:

for (auto o : gameObjects)
    o->update(deltaTime);

Answer 2

You can use the same code you have, but use mem_fun instead of mem_fun_ref

std::for_each(gameObjects.begin(), gameObjects.end(),
    std::mem_fun(&GameObject::update));

Answer 3

As an alternative to std::for_each , if your compiler and policy allows for it, you can use C++' range based for :

for (auto p : gameObjects) p->update();

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_{This feature was added with C++11, which is the current C++ standard. Not all compiler(-versions) may support it yet.}