E.4: Design your error-handling strategy around invariants
E.4:围绕不变量设计错误处理策略
Reason(原因)
To use an object it must be in a valid state (defined formally or informally by an invariant) and to recover from an error every object not destroyed must be in a valid state.
为了使用对象,它一定要处于有效状态(通过不变量形式化或非形式化定义)并且为了从错误中恢复,所有没有销毁的对象必须处于有效状态。
Note(注意)
An invariant is a logical condition for the members of an object that a constructor must establish for the public member functions to assume.
不变量是一个适用于对象成员的逻辑条件,这个条件必须有构造函数建立,可以作为公有成员函数的前提条件。
Enforcement(实施建议)
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E.5: Let a constructor establish an invariant, and throw if it cannot
E.5:让构造函数建立不变量,如果不能就抛异常
Reason(原因)
Leaving an object without its invariant established is asking for trouble. Not all member functions can be called.
建立一个对象却没有建立不变量是在找麻烦。不是所有成员函数都是可以被调用的。
Example(示例)
The class invariant - here stated as a comment - is established by the constructors. new throws if it cannot allocate the required memory. The operators, notably the subscript operator, relies on the invariant.
See also: If a constructor cannot construct a valid object, throw an exception
类不变量-这里通过注释声明-通过构造函数建立了。如果不能分配要求的内存,new操作会抛出异常。运算符,特别是下标运算符依靠不变量。参见:如果不能构建有效的对象,就抛出异常。
Enforcement(实施建议)
Flag classes with private state without a constructor (public, protected, or private).
标记那些没有构造函数(公有的,私有的或保护的)却有私有成员的类。
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