问题描述

boost 库中是否有 C++1x 的 std::unique_ptr 等价类?我正在寻找的行为是能够拥有异常安全的工厂函数，就像这样......

Is there some equivalent class for C++1x's std::unique_ptr in the boost libraries? The behavior I'm looking for is being able to have an exception-safe factory function, like so...

std::unique_ptr<Base> create_base()
{
    return std::unique_ptr<Base>(new Derived);
}

void some_other_function()
{
    std::unique_ptr<Base> b = create_base();

    // Do some stuff with b that may or may not throw an exception...

    // Now b is destructed automagically.
}

现在，我正在使用这个 hack，这似乎是我目前所能得到的最好的......

Right now, I'm using this hack, which seems like the best I can get at this point...

Base* create_base()
{
    return new Derived;
}

void some_other_function()
{
    boost::scoped_ptr<Base> b = create_base();

    // Do some stuff with b that may or may not throw an exception...

    // Now b is deleted automagically.
}

推荐答案

如果没有 C++0x，就不可能创建像 unique_ptr 这样的东西(它是标准库的一部分，所以 Boost 不不需要提供).

It's not possible to create something like unique_ptr without C++0x (where it's part of the standard library, and so Boost doesn't need to provide it).

特别是如果没有右值引用(C++0x 中的一个特性)，unique_ptr 的健壮实现是不可能的，无论有没有 Boost.

Specifically without rvalue references, which are a feature in C++0x, a robust implementation of unique_ptr is impossible, with or without Boost.

在 C++03 中，有几种可能的替代方案，尽管每种方案都有其缺陷.

In C++03, there are a few possible alternatives, although each have their flaws.

• boost::shared_ptr 可能是功能方面最简单的替代品.你可以安全地在任何地方使用它，否则它会使用 unique_ptr 并且它会工作.由于添加了引用计数，它的效率不会那么高.但是，如果您正在寻找能够处理 unique_ptr 可以做的所有事情的简单的替代品，这可能是您最好的选择.(当然，shared_ptr 也可以做更多的事情，但它也可以简单地用作 unique_ptr 的替代品.)
• boost::scoped_ptr 与 unique_ptr 类似，但不允许转让所有权.只要智能指针旨在在其整个生命周期内保持独占所有权，它就可以很好地工作.
• std::auto_ptr 的工作原理与 unique_ptr 非常相似，但有一些限制，主要是它不能存储在标准库容器中.如果您只是在寻找一个允许所有权转移的指针，但并不打算将其存储在容器中或四处复制，那么这可能是一个不错的选择.

• boost::shared_ptr is probably the simplest replacement in terms of capabilites. You can safely use it anywhere you'd otherwise use a unique_ptr and it'd work. It just wouldn't be as efficient, because of the added reference counting. But if you're looking for a simple drop-in replacement that's able to handle everything unique_ptr can do, this is probably your best bet. (Of course, a shared_ptr can do a lot more as well, but it can also simply be used as a drop-in replacement for unique_ptr.)
• boost::scoped_ptr is similar to unique_ptr but does not allow transfer of ownership. It works great as long as the smart pointer is meant to retain exclusive ownership throughout its lifetime.
• std::auto_ptr works very similar to unique_ptr, but has a few limitations, mainly that it can not be stored in standard library containers. If you're simply looking for a pointer that allows transfer of ownership, but which is not meant to be stored in containers or copied around, this is probably a good bet.

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