如何在堆栈上创建多态对象? [英] How can I create a polymorphic object on the stack?

问题描述

如何在堆栈上分配多态对象?我正在尝试做类似的事情(试图避免用new分配堆)?

How do I allocate a polymorphic object on the stack? I'm trying to do something similar to (trying to avoid heap allocation with new)?:

A* a = NULL;

switch (some_var)
{
case 1:
    a = A();
    break;
case 2:
    a = B(); // B is derived from A
    break;
default:
    a = C(); // C is derived from A
    break;
}

推荐答案

由于无法在条件块中创建自动对象或临时对象，因此无法构造单个函数以使其工作，因为阻止.

You can't structure a single function to work like that, since automatic or temporary objects created inside a conditional block can't have their lifetimes extended into the containing block.

我建议将多态行为重构为一个单独的函数:

I'd suggest refactoring the polymorphic behaviour into a separate function:

void do_something(A&&);

switch (some_var)
{
case 1:
    do_something(A());
    break;
case 2:
    do_something(B()); // B is derived from A
    break;
default:
    do_something(C()); // C is derived from A
    break;
}

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