2 template <typename Service>
3 bool has_service() const
4 {
5 boost::asio::detail::mutex::scoped_lock lock(mutex_);
6
7 boost::asio::io_service::service* service = first_service_;
8 while (service)
9 {
10 if (service_id_matches(*service, Service::id))
11 return true;
12 service = service->next_;
13 }
14
15 return false;
16 }
bool has_service(io_service& ios)
{
// Check that Service meets the necessary type requirements.
(void)static_cast<io_service::service*>(static_cast<Service*>(0));
(void)static_cast<const io_service::id*>(&Service::id);
return ios.service_registry_->template has_service<Service>();
}
下面是测试例子,在VS2005中编译通过。原来,函数使用的时候,可以完全指定模板函数定义。
2 {
3 public:
4 static int getI()
5 {
6 return 100;
7 }
8 };
9 class V
10 {
11 public:
12 template<class K>
13 void PrintK()
14 {
15 cout<<K::getI()<<endl;
16 }
17 };
18 void m()
19 {
20 V v;
21 v.template PrintK<VV>();
22 }
ANSI C++ '03
14.2 Names of template specializations
4 When the name of a member template specialization appears after . or -> in a postfix-expression, or after
nested-name-specifier in a qualified-id, and the postfix-expression or qualified-id explicitly depends on a
template-parameter (14.6.2), the member template name must be prefixed by the keyword template.
Otherwise the name is assumed to name a non-template. [Example:
class X {
public:
template<size_t> X* alloc();
template<size_t> static X* adjust();
};
template<class T> void f(T* p)
{
T* p1 = p->alloc<200>();
// ill-formed: < means less than
T* p2 = p->template alloc<200>();
// OK: < starts template argument list
T::adjust<100>();
// ill-formed: < means less than
T::template adjust<100>();
// OK: < starts template argument list
}