多个类型名称的部分模板专门化 [英] Partial template specialization for more than one typename

问题描述

在下面的代码中，我想考虑具有 void 的函数（ Op 考虑返回 true 。类型 Retval 和 Op 的返回值总是匹配。我不能使用这里显示的类型traits区分，并尝试创建基于 Retval 的部分模板专门化失败，由于存在其他模板变量， code> Op 和 Args 。

In the following code, I want to consider functions (Ops) that have void return to instead be considered to return true. The type Retval, and the return value of Op are always matching. I'm not able to discriminate using the type traits shown here, and attempts to create a partial template specialization based on Retval have failed due the presence of the other template variables, Op and Args.

变量在模板专业化而不会得到错误？是否有其他方法根据 Op ？的返回类型来改变行为？

How do I specialize only some variables in a template specialization without getting errors? Is there any other way to alter behaviour based on the return type of Op?

template <typename Retval, typename Op, typename... Args>
Retval single_op_wrapper(
        Retval const failval,
        char const *const opname,
        Op const op,
        Cpfs &cpfs,
        Args... args) {
    try {
        CallContext callctx(cpfs, opname);
        Retval retval;
        if (std::is_same<bool, Retval>::value) {
            (callctx.*op)(args...);
            retval = true;
        } else {
            retval = (callctx.*op)(args...);
        }
        assert(retval != failval);
        callctx.commit(cpfs);
        return retval;
    } catch (CpfsError const &exc) {
        cpfs_errno_set(exc.fserrno);
        LOGF(Info, "Failed with %s", cpfs_errno_str(exc.fserrno));
    }
    return failval;
}

推荐答案

template <typename Retval, typename Op, typename... Args>
Retval single_op_wrapper(
        Retval const failval,
        char const *const opname,
        Op const op,
        Cpfs &cpfs,
        Args... args) {
    try {
        CallContext callctx(cpfs, opname);
        Retval retval;
        if (std::is_same<bool, Retval>::value) {
            (callctx.*op)(args...);
            retval = true;
        } else {
            retval = (callctx.*op)(args...);
        }
        assert(retval != failval);
        callctx.commit(cpfs);
        return retval;
    } catch (CpfsError const &exc) {
        cpfs_errno_set(exc.fserrno);
        LOGF(Info, "Failed with %s", cpfs_errno_str(exc.fserrno));
    }
    return failval;
}
template<typename Op, typename... Args> void single_op_wrapper<void, Op, Args>(...) {
    ...
}

b $ b

编辑：忘记你正在写一个函数，而不是一个类。

Forgot you were writing a function, not a class.

这篇关于多个类型名称的部分模板专门化的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！