ES.25: Declare an object const or constexpr unless you want to modify its value later on
ES.25:如果没有考虑修改对象的值，就将对象定义为const或者constexpr
Reason（原因）
That way you can't change the value by mistake. That way may offer the compiler optimization opportunities.
这么做之后，就不会发生因为错误而修改变量值的情况。这种方式还增加了编译优化的机会。
Example（示例）
void f(int n)
{
const int bufmax = 2 * n + 2; // good: we can't change bufmax by accident
int xmax = n; // suspicious: is xmax intended to change?
// ...
}
Enforcement（实施建议）
Look to see if a variable is actually mutated, and flag it if not. Unfortunately, it may be impossible to detect when a non-const was not intended to vary (vs when it merely did not vary).
观察变量是否可变，如果不是就标记它。不幸的是，可能很难检测什么时候一个非常量没有修改的意图（或者它仅仅是还没有修改）。
原文链接
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es25-declare-an-object-const-or-constexpr-unless-you-want-to-modify-its-value-later-on
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