C++核心准则T.60:最小化模板对上下文的依赖

T.60: Minimize a template's context dependencies

T.60:最小化模板对上下文的依赖

Reason（原因）

Eases understanding. Minimizes errors from unexpected dependencies. Eases tool creation.

让理解更容易。尽量减少由于意外的依赖引发的错误。方便工具生成。

Example（示例）

template<typename C>
void sort(C& c)
{
    std::sort(begin(c), end(c)); // necessary and useful dependency
}

template<typename Iter>
Iter algo(Iter first, Iter last)
{
    for (; first != last; ++first) {
        auto x = sqrt(*first); // potentially surprising dependency: which sqrt()?
        helper(first, x);      // potentially surprising dependency:
                               // helper is chosen based on first and x
        TT var = 7;            // potentially surprising dependency: which TT?
    }
}

Note（注意）

Templates typically appear in header files so their context dependencies are more vulnerable to #include order dependencies than functions in .cpp files.

模板通常出现在头文件中，相比在CPP文件中的情况，它们的上下文依赖会更容易受到#include次序的影响。

Note（注意）

Having a template operate only on its arguments would be one way of reducing the number of dependencies to a minimum, but that would generally be unmanageable. For example, algorithms usually use other algorithms and invoke operations that do not exclusively operate on arguments. And don't get us started on macros!

让模板操作仅仅操作参数是一种将依赖个数减少到最小的一种方式。但是那样通常会无法实现。例如，算法通常会使用其他算法并调用无法对参数进行排他操作的操作。