无法理解 ns-3 源代码中 getter 方法的 Constructor() 语法

Question

下面是代码片段


TypeId
UdpEchoClient::GetTypeId (void)
{
  static TypeId tid = TypeId ("ns3::UdpEchoClient")
    .SetParent<Application> ()
    .SetGroupName("Applications")
    .AddConstructor<UdpEchoClient> ()
    .AddAttribute ("MaxPackets", 
                   "The maximum number of packets the application will send",
                   UintegerValue (100),
                   MakeUintegerAccessor (&UdpEchoClient::m_count),
                   MakeUintegerChecker<uint32_t> ())
    .AddAttribute ("Interval", 
                   "The time to wait between packets",
                   TimeValue (Seconds (1.0)),
                   MakeTimeAccessor (&UdpEchoClient::m_interval),
                   MakeTimeChecker ())
    .AddAttribute ("RemoteAddress", 
                   "The destination Address of the outbound packets",
                   AddressValue (),
                   MakeAddressAccessor (&UdpEchoClient::m_peerAddress),
                   MakeAddressChecker ())
    .AddAttribute ("RemotePort", 
                   "The destination port of the outbound packets",
                   UintegerValue (0),
                   MakeUintegerAccessor (&UdpEchoClient::m_peerPort),
                   MakeUintegerChecker<uint16_t> ())
    .AddAttribute ("PacketSize", "Size of echo data in outbound packets",
                   UintegerValue (100),
                   MakeUintegerAccessor (&UdpEchoClient::SetDataSize,
                                         &UdpEchoClient::GetDataSize),
                   MakeUintegerChecker<uint32_t> ())
    .AddTraceSource ("Tx", "A new packet is created and is sent",
                     MakeTraceSourceAccessor (&UdpEchoClient::m_txTrace),
                     "ns3::Packet::TracedCallback")
    .AddTraceSource ("Rx", "A packet has been received",
                     MakeTraceSourceAccessor (&UdpEchoClient::m_rxTrace),
                     "ns3::Packet::TracedCallback")
    .AddTraceSource ("TxWithAddresses", "A new packet is created and is sent",
                     MakeTraceSourceAccessor (&UdpEchoClient::m_txTraceWithAddresses),
                     "ns3::Packet::TwoAddressTracedCallback")
    .AddTraceSource ("RxWithAddresses", "A packet has been received",
                     MakeTraceSourceAccessor (&UdpEchoClient::m_rxTraceWithAddresses),
                     "ns3::Packet::TwoAddressTracedCallback")
  ;
  return tid;
}

尤其是下面这个片段

static TypeId tid = TypeId ("ns3::UdpEchoClient")
    .SetParent<Application> ()
    .SetGroupName("Applications")

在此 SetParent() 方法中 "Application" 是什么？ SetParent() 的声明是：

TypeId SetParent (TypeId tid);
and
template <typename T> TypeId SetParent (void);

有人可以解释一下这个 GetTypeId() 吗，在 TypeId 构造函数上使用嵌套点 (.) 运算符是怎么回事？

这里是 link 文件 :
[1] https://github.com/signetlabdei/quic-ns-3/blob/master/src/applications/model/udp-echo-client.cc

[2] https://github.com/signetlabdei/quic-ns-3/blob/master/src/core/model/type-id.h

[3] https://github.com/signetlabdei/quic-ns-3/blob/master/src/core/model/type-id.cc

[4] https://github.com/signetlabdei/quic-ns-3/blob/master/src/applications/model/udp-echo-client.h

Answer 1

Can somebody explain this GetTypeId(), what is going on here with nested dot(.) operators over a TypeId constructor?

如果你查看头文件中符号的声明，你会注意到所有这些 "nested dot operators" 只是 class TypeId return 的方法正在 TypeId:

template <typename T> TypeId SetParent (void);

如果您查看方法的源代码：

TypeId 
TypeId::SetParent (TypeId tid)
{
  NS_LOG_FUNCTION (this << tid.GetUid ());
  IidManager::Get ()->SetParent (m_tid, tid.m_tid);
  return *this; //here the copy takes place
}

很明显它 return 是它自己的副本。

但为什么它 return 是它自己的副本？当再次查看头文件时，很明显 struct TypeId 只有一个值：

class TypeId
{
// lots and lots of method declarations
// [...]
/** The TypeId value. */ 
  uint16_t m_tid;
};

因此文案只是实现算子嵌套的一个工具

那么它有什么作用呢？因为我没有写过这段代码，所以我不能 100% 确定，但对我来说，它似乎包含一些关于传递类型的元信息，您可以在运行时更改这些信息（例如更改构造函数或超级 class）

无法理解 ns-3 源代码中 getter 方法的 Constructor() 语法

Unable to understand Constructor() syntax of a getter method in ns-3 source code

c++

ns-3