想象一下,我有一份工作要做,可以通过三种不同的方式来完成：缓慢而痛苦,但却是安全的方式;鉴于你有资源1,适度痛苦的方式;以及一种快速简便的方法,它需要Resource1和Resource2.现在,这些资源是宝贵的,所以我将它们包装成RAII实现ResNHolders并写下这样的东西：
void DoTheJob(Logger& log/*,some other params */) {
try {
Res1Holder r1(/* arguments for creating resource #1 */);
try {
Res2Holder r2(/* arguments */);
DoTheJobQuicklyAndEasily(log,r1,r2);
}
catch (Res2InitializationException& e) {
log.log("Can't obtain resource 2,that'll slowdown us a bit");
DoTheJobWithModerateSuffering(log,r1);
}
}
catch (Res1InitializationException& e) {
log.log("Can't obtain resource 1,using fallback");
DoTheJobTheSlowAndPainfulWay(log);
}
}
“DoTheJobXxx()”引用了Logger / ResNHolder,因为它们是不可复制的.我这样做太笨拙了吗？有没有其他聪明的方法来构建函数？
解决方法
我认为你的代码会很好,但这里有一个可以考虑的替代方案：
void DoTheJob(Logger &log/*,args*/)
{
std::unique_ptr<Res1Holder> r1 = acquireRes1(/*args*/);
if (!r1) {
log.log("Can't acquire resource 1,using fallback");
DoTheJobTheSlowAndPainfulWay(log);
return;
}
std::unique_ptr<Res2Holder> r2 = acquireRes2(/*args*/);
if (!r2) {
log.log("Can't acquire resource 2,that'll slow us down a bit.");
DoTheJobWithModerateSuffering(log,*r1);
return;
}
DoTheJobQuicklyAndEasily(log,*r1,*r2);
}
当资源无法初始化时,acquireRes函数返回null unique_ptr：
std::unique_ptr<Res1Holder> acquireRes1()
{
try {
return std::unique_ptr<Res1Holder>(new Res1Holder());
}
catch (Res1InitializationException& e) {
return std::unique_ptr<Res1Holder>();
}
}
std::unique_ptr<Res2Holder> acquireRes2()
{
try {
return std::unique_ptr<Res2Holder>(new Res2Holder());
}
catch (Res2InitializationException& e) {
return std::unique_ptr<Res2Holder>();
}
}
