[Muduo网络库源码分析] (11) base/Types.h_基本类型声明

基本类型声明

功能：为网络库提供基本的类型

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知识点：

• stirng 的三种实现方式：

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用途：

可用与类型转换和string的高效使用

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代码及分析：

Types.h

#ifndef MUDUO_BASE_TYPES_H#define MUDUO_BASE_TYPES_H#include <stdint.h>#ifdef MUDUO_STD_STRING#include <string>#else  // !MUDUO_STD_STRING#include <ext/vstring.h>#include <ext/vstring_fwd.h>#endif#ifndef NDEBUG#include <assert.h>#endif////// The most common stuffs.///namespace muduo{#ifdef MUDUO_STD_STRING//无特殊处理的C++实现方式using std::string;#else  // !MUDUO_STD_STRING//利用string的短字符优化实现方式typedef __gnu_cxx::__sso_string string;#endif// Taken from google-protobuf stubs/common.h//// Protocol Buffers - Google's data interchange format// Copyright 2008 Google Inc.  All rights reserved.// http://code.google.com/p/protobuf///// Redistribution and use in source and binary forms, with or without// modification, are permitted provided that the following conditions are// met:////     * Redistributions of source code must retain the above copyright// notice, this list of conditions and the following disclaimer.//     * Redistributions in binary form must reproduce the above// copyright notice, this list of conditions and the following disclaimer// in the documentation and/or other materials provided with the// distribution.//     * Neither the name of Google Inc. nor the names of its// contributors may be used to endorse or promote products derived from// this software without specific prior written permission.//// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.// Author: [e-mail] (Kenton Varda) and others//// Contains basic types and utilities used by the rest of the library.//// Use implicit_cast as a safe version of static_cast or const_cast// for upcasting in the type hierarchy (i.e. casting a pointer to Foo// to a pointer to SuperclassOfFoo or casting a pointer to Foo to// a const pointer to Foo).// When you use implicit_cast, the compiler checks that the cast is safe.// Such explicit implicit_casts are necessary in surprisingly many// situations where C++ demands an exact type match instead of an// argument type convertable to a target type.//// The From type can be inferred, so the preferred syntax for using// implicit_cast is the same as for static_cast etc.:////   implicit_cast<ToType>(expr)//// implicit_cast would have been part of the C++ standard library,// but the proposal was submitted too late.  It will probably make// its way into the language in the future.//类型强转，implicit_cast只能执行up-cast，派生类->基类//这里模拟了boost库里面的implicit_casttemplate<typename To, typename From>inline To implicit_cast(From const &f){  return f;}// When you upcast (that is, cast a pointer from type Foo to type// SuperclassOfFoo), it's fine to use implicit_cast<>, since upcasts// always succeed.  When you downcast (that is, cast a pointer from// type Foo to type SubclassOfFoo), static_cast<> isn't safe, because// how do you know the pointer is really of type SubclassOfFoo?  It// could be a bare Foo, or of type DifferentSubclassOfFoo.  Thus,// when you downcast, you should use this macro.  In debug mode, we// use dynamic_cast<> to double-check the downcast is legal (we die// if it's not).  In normal mode, we do the efficient static_cast<>// instead.  Thus, it's important to test in debug mode to make sure// the cast is legal!//    This is the only place in the code we should use dynamic_cast<>.// In particular, you SHOULDN'T be using dynamic_cast<> in order to// do RTTI (eg code like this://    if (dynamic_cast<Subclass1>(foo)) HandleASubclass1Object(foo);//    if (dynamic_cast<Subclass2>(foo)) HandleASubclass2Object(foo);// You should design the code some other way not to need this.//进行down_cast 基类->派生类转换，并检查转换是否安全template<typename To, typename From>     // use like this: down_cast<T*>(foo);inline To down_cast(From* f)                     // so we only accept pointers{  // Ensures that To is a sub-type of From *.  This test is here only  // for compile-time type checking, and has no overhead in an  // optimized build at run-time, as it will be optimized away  // completely.  if (false)  {    implicit_cast<From*, To>(0);  }#if !defined(NDEBUG) && !defined(GOOGLE_PROTOBUF_NO_RTTI)  //dynamic_cast检查该类型转换是否安全  assert(f == NULL || dynamic_cast<To>(f) != NULL);  // RTTI: debug mode only!#endif  return static_cast<To>(f);}}#endif