C++核心准则T.3:使用模板表现容器和范围

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T.3: Use templates to express containers and ranges

T.3:使用模板表现容器和范围

Reason（原因）

Containers need an element type, and expressing that as a template argument is general, reusable, and type safe. It also avoids brittle or inefficient workarounds. Convention: That's the way the STL does it.

容器需要知道元素类型，将元素类型表示为模板参数是通行，可重用和类型安全的方式。它可以避免脆弱性和低效的变通。做为惯例，STL就是这么做的。

Example（示例）

template<typename T>
    // requires Regular<T>
class Vector {
    // ...
    T* elem;   // points to sz Ts
    int sz;
};

Vector<double> v(10);
v[7] = 9.9;

Example, bad（反面示例）

class Container {
    // ...
    void* elem;   // points to size elements of some type
    int sz;
};

Container c(10, sizeof(double));
((double*) c.elem)[7] = 9.9;

This doesn't directly express the intent of the programmer and hides the structure of the program from the type system and optimizer.

Hiding the void* behind macros simply obscures the problems and introduces new opportunities for confusion.

这段代码没有直接表达程序员的意图并对类型系统和优化器隐藏程序结构。用宏定义掩盖void*只会模糊化问题并进一步增加混淆的机会。

Exceptions: If you need an ABI-stable interface, you might have to provide a base implementation and express the (type-safe) template in terms of that. See Stable base.

例外：如果你需要ABI稳定的接口，你可能必须提供一个基础实现并按照其概念表现模板。

Enforcement（实施建议）

• Flag uses of void*s and casts outside low-level implementation code
• 标记使用void*并在外面的实现代码中使用低水平类型转换的情况。

原文链接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#t3-use-templates-to-express-containers-and-ranges