C++核心準(zhǔn)則C.145:通過指針或引用訪問多態(tài)對(duì)象

C.145: Access polymorphic objects through pointers and references

C.145:通過指針或引用訪問多態(tài)對(duì)象

Reason（原因）

If you have a class with a virtual function, you don't (in general) know which class provided the function to be used.

如果類有虛函數(shù)，通常不會(huì)知道使用的函數(shù)具體是由那個(gè)（派生）類提供的。

Example（示例）

struct B { int a; virtual int f(); virtual ~B() = default };
struct D : B { int b; int f() override; };

void use(B b)
{
    D d;
    B b2 = d;   // slice
    B b3 = b;
}

void use2()
{
    D d;
    use(d);   // slice
}

Both?ds are sliced.

兩個(gè)(函數(shù)中的)d都被切斷了（因?yàn)榕缮悓?duì)象向基類對(duì)象賦值，譯者注）

Exception (例外)

You can safely access a named polymorphic object in the scope of its definition, just don't slice it.

你可以在多態(tài)對(duì)象被定義的作用域中通過變量名安全地使用它，只要注意不被切斷就行。

void use3()
{
    D d;
    d.f();   // OK
}

See also（參見）

A polymorphic class should suppress copying（多態(tài)類應(yīng)該抑制復(fù)制）

Enforcement

Flag all slicing.（標(biāo)記發(fā)生數(shù)據(jù)切斷的操作）

原文鏈接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c145-access-polymorphic-objects-through-pointers-and-references

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