I.1: Make interfaces explicit（使接口清晰明确）
Reason（原因）
Correctness. Assumptions not stated in an interface are easily overlooked and hard to test.
正确性。在接口中没有说明的假设很容易被忽视且难于测试。
Example, bad（反面示例）
Controlling the behavior of a function through a global (namespace scope) variable (a call mode) is implicit and potentially confusing. For example:
通过全局（命名空间范围）变量（调用模式）控制函数行为的方式是隐晦且不易理解的，例如：
int round(double d)
{
return (round_up) ? ceil(d) : d; // don't: "invisible" dependency
}It will not be obvious to a caller that the meaning of two calls of round (7.2) might give different results.
调用者不容易理解两次调用 round(7.2) 可能返回不同的结果。
Exception（例外）
Sometimes we control the details of a set of operations by an environment variable, e.g., normal vs. verbose output or debug vs. optimized. The use of a non-local control is potentially confusing, but controls only implementation details of otherwise fixed semantics.
有时我们通过环境变量控制一套操作的细节。例如，正常输出还是详细输出，也可能是调试还是优化。使用非局部控制的做法可能会难于理解，只可以应用在其他固定语义的实现细节的情况。
Example, bad（反面示例）
Reporting through non-local variables (e.g., errno) is easily ignored.
For example:
通过非局部变量报告（例如错误编码）很容易被忽略。例如：
// don't: no test of printf's return value fprintf(connection, "logging: %d %d %d\n", x, y, s);
What if the connection goes down so that no logging output is produced? See I.???.
如果连接被关闭而导致没有日志输出怎么办？参考I.???
Alternative: Throw an exception. An exception cannot be ignored.
可选项：抛出异常。异常不会被忽略。
Alternative formulation: Avoid passing information across an interface through non-local or implicit state. Note that non-const member functions pass information to other member functions through their object's state.
另一种说法：避免会用非局部或隐含状态通过接口传递信息。注意非const成员通过对象状态函数向另外一个成员函数传递信息的情况。
Alternative formulation: An interface should be a function or a set of functions. Functions can be template functions and sets of functions can be classes or class templates.
另一种说法：接口应该是一个或一组函数。接口可以是模板函数，函数组可以是类和类模板。
Enforcement（实施建议）
- (Simple) A function should not make control-flow decisions based on the values of variables declared at namespace scope.
（简单）函数不应该根据命名空间范围中的变量决定控制流。
- (Simple) A function should not write to variables declared at namespace scope.
（简单）函数不应该改写定义于命名空间范围的变量。
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