使用concepts实现接口隔离原则

本例有一个打印机类，部分打印机可打印，部分打印机可扫描，部分打印机可传真。
作者本想设计一个大的接口，用来同时print, scan和fax。
但是后来运用接口隔离原则，实现最小接口。print,scan和fax。
然后使用装饰器模式对print,scan和fax进行组合。
作者使用传统的纯虚函数和override来实现。
本例使用concept来实现。
代码如下，
CMakeLists.txt

cmake_minimum_required(VERSION 2.6)

if(APPLE)
    message(STATUS "This is Apple, do nothing.")
    set(CMAKE_MACOSX_RPATH 1)
    set(CMAKE_PREFIX_PATH /Users/aabjfzhu/software/vcpkg/ports/cppwork/vcpkg_installed/x64-osx/share )
elseif(UNIX)
    message(STATUS "This is linux, set CMAKE_PREFIX_PATH.")
    set(CMAKE_PREFIX_PATH /vcpkg/ports/cppwork/vcpkg_installed/x64-linux/share)
endif(APPLE)

project(interface_seg)

set(CMAKE_CXX_STANDARD 20)

add_definitions(-g)

find_package(ZLIB)

find_package(OpenCV REQUIRED )
find_package(Arrow CONFIG REQUIRED)

find_package(unofficial-brotli REQUIRED)
find_package(unofficial-utf8proc CONFIG REQUIRED)
find_package(Thrift CONFIG REQUIRED)

find_package(glog REQUIRED)

find_package(OpenSSL REQUIRED)

find_package(Boost REQUIRED COMPONENTS
    system
    filesystem
    serialization
    program_options
    thread
    )

find_package(DataFrame REQUIRED)

if(APPLE)
    MESSAGE(STATUS "This is APPLE, set INCLUDE_DIRS")
set(INCLUDE_DIRS ${Boost_INCLUDE_DIRS} /usr/local/include /usr/local/iODBC/include /opt/snowflake/snowflakeodbc/include/ ${CMAKE_CURRENT_SOURCE_DIR}/../include/ ${CMAKE_CURRENT_SOURCE_DIR}/../../../include)
elseif(UNIX)
    MESSAGE(STATUS "This is linux, set INCLUDE_DIRS")
    set(INCLUDE_DIRS ${Boost_INCLUDE_DIRS} /usr/local/include ${CMAKE_CURRENT_SOURCE_DIR}/../include/   ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/)
endif(APPLE)


if(APPLE)
    MESSAGE(STATUS "This is APPLE, set LINK_DIRS")
    set(LINK_DIRS /usr/local/lib /usr/local/iODBC/lib /opt/snowflake/snowflakeodbc/lib/universal)
elseif(UNIX)
    MESSAGE(STATUS "This is linux, set LINK_DIRS")
    set(LINK_DIRS ${Boost_INCLUDE_DIRS} /usr/local/lib /vcpkg/ports/cppwork/vcpkg_installed/x64-linux/lib)
endif(APPLE)

if(APPLE)
    MESSAGE(STATUS "This is APPLE, set ODBC_LIBS")
    set(ODBC_LIBS iodbc iodbcinst)
elseif(UNIX)
    MESSAGE(STATUS "This is linux, set LINK_DIRS")
    set(ODBC_LIBS odbc odbcinst ltdl)
endif(APPLE)

include_directories(${INCLUDE_DIRS})
LINK_DIRECTORIES(${LINK_DIRS})

file( GLOB test_file_list ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp) 

file( GLOB APP_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/../impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../include/*.h ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/arr_/impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/http/impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/yaml/impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/df/impl/*.cpp ${CMAKE_CURRENT_SOURCE_DIR}/../../../include/death_handler/impl/*.cpp)

add_library(${PROJECT_NAME}_lib SHARED ${APP_SOURCES} ${test_file})
target_link_libraries(${PROJECT_NAME}_lib ${Boost_LIBRARIES} ZLIB::ZLIB glog::glog DataFrame::DataFrame ${OpenCV_LIBS})
target_link_libraries(${PROJECT_NAME}_lib OpenSSL::SSL OpenSSL::Crypto libgtest.a pystring libyaml-cpp.a libgmock.a ${ODBC_LIBS} libnanodbc.a pthread dl backtrace libzstd.a libbz2.a libsnappy.a re2::re2 parquet lz4 unofficial::brotli::brotlidec-static unofficial::brotli::brotlienc-static unofficial::brotli::brotlicommon-static utf8proc thrift::thrift  arrow arrow_dataset)

foreach( test_file ${test_file_list} )
    file(RELATIVE_PATH filename ${CMAKE_CURRENT_SOURCE_DIR} ${test_file})
    string(REPLACE ".cpp" "" file ${filename})
    add_executable(${file}  ${test_file})
    target_link_libraries(${file} ${PROJECT_NAME}_lib)
endforeach( test_file ${test_file_list})

test/interface_seg_test.cpp

#include "death_handler/death_handler.h"
#include "json/json.hpp"
#include 
#include "machine.hpp"
#include 
#include "df/df.h"

using json = nlohmann::json;

int main(int argc, char** argv) {
    FLAGS_log_dir = "./";
    FLAGS_alsologtostderr = true;
    // 日志级别 INFO, WARNING, ERROR, FATAL 的值分别为0、1、2、3
    FLAGS_minloglevel = 0;

    Debug::DeathHandler dh;

    google::InitGoogleLogging("./logs.log");
    testing::InitGoogleTest(&argc, argv);
    int ret = RUN_ALL_TESTS();
    return ret;
}

GTEST_TEST(InterfaceSegTests, InterfaceSeg) {
    Document doc {"Raw Document"};
    auto p_imp = PrintImpl{};
    auto s_imp = ScannerImpl{};

    Printer p{p_imp};
    p.print(doc);
    
    Machine m{p_imp, s_imp};
    m.print(doc);
    m.scan(doc);
}

include/machine.hpp

#ifndef _FREDRIC_MACHINE_HPP_
#define _FREDRIC_MACHINE_HPP_

#include 
#include 
#include 
#include 

struct Document {
    std::string text;
};

template 
concept PrintType = requires (const T value) {
    value.print(std::declval());
};

template 
concept ScannerType = requires (const T value) {
    value.scan(std::declval());
};

template 
concept FaxType = requires (const T value) {
    value.fax(std::declval());
};

template 
struct Printer {
    PrintT const& printer;
    Printer(PrintT const& printer_): printer{printer_} {}

    void print(Document& doc) const{
        printer.print(doc);
    }
};

template 
struct Machine {
    PrintT const& printer;
    ScanT const& scanner;

    Machine(PrintT const& printer_, ScanT const& scanner_): printer{printer_}, scanner{scanner_} {}

    void print(Document& doc) const {
        printer.print(doc);
    }

    void scan(Document& doc) const {
        scanner.scan(doc);
    }
};

struct PrintImpl {
    void print(Document& doc) const{
        std::cout << "PrintImpl print: " << doc.text << "\n";
    }
};

struct ScannerImpl {
    void scan(Document& doc) const{
        std::cout << "ScannerImpl scan: " << doc.text << "\n";
    }
};
#endif

程序输出如下，

image.png