Here are step-by-step guides for installing LLVM, CMake, and Ninja on MacOS using Homebrew:

Installing LLVM:

1. Open a terminal on your MacOS system and run the following command to update Homebrew:
   brew update
2. Use the brew search command to search for LLVM in the Homebrew package repository:
   brew search llvm
3. This will show a list of LLVM packages available in the Homebrew package repository. To install LLVM, run the brew install command and specify the name of the LLVM package that you want to install. For example, to install the latest version of LLVM, you can use the following command:
   brew install llvm
4. This will download and install LLVM on your MacOS system. You can verify the installation by running the llvm-config command in the terminal:
   llvm-config --version

Installing CMake:

1. Open a terminal on your MacOS system and run the following command to update Homebrew:
   brew update
2. Use the brew search command to search for CMake in the Homebrew package repository:
   brew search cmake
3. This will show a list of CMake packages available in the Homebrew package repository. To install CMake, run the brew install command and specify the name of the CMake package that you want to install. For example, to install the latest version of CMake, you can use the following command:
   brew install cmake
4. This will download and install CMake on your MacOS system. You can verify the installation by running the cmake command in the terminal:
   cmake --version

Installing Ninja:

1. Open a terminal on your MacOS system and run the following command to update Homebrew:
   brew update
2. Use the brew search command to search for Ninja in the Homebrew package repository:
   brew search ninja
3. This will show a list of Ninja packages available in the Homebrew package repository. To install Ninja, run the brew install command and specify the name of the Ninja package that you want to install. For example, to install the latest version of Ninja, you can use the following command:
   brew install ninja
4. This will download and install Ninja on your MacOS system. You can verify the installation by running the ninja command in the terminal:
   ninja --version

That’s it! You have successfully installed LLVM, CMake, and Ninja on your MacOS system using Homebrew. You can now use these tools for C++ development on your MacOS system

Here is an example CMakeLists.txt file for CMake, and an accompanying build.ninja file for Ninja:

CMakeLists.txt:

cmake_minimum_required(VERSION 3.10) 
project(my_project VERSION 1.0) 

# Specify the C++ language standard 
set(CMAKE_CXX_STANDARD 14) 
set(CMAKE_CXX_STANDARD_REQUIRED True) 

# Specify the source files for the project 
set(SOURCES main.cpp foo.cpp bar.cpp ) 

# Add an executable target for the project 
add_executable(my_project ${SOURCES}) 

# Install the executable to the bin directory 
install(TARGETS my_project DESTINATION bin)

build.ninja:

# CMake configuration 
cmake_minimum_required(VERSION 3.10) 
project(my_project VERSION 1.0) 
# Ninja build rules 
rule build_my_project command = clang++ -o $out $in description = Building $out build my_project: build_my_project main.cpp foo.cpp bar.cpp

This CMakeLists.txt file specifies the minimum required CMake version, the name and version of the project, the C++ language standard, and the source files for the project. It also adds an executable target for the project and specifies that the executable should be installed to the bin directory.

The build.ninja file specifies a build rule for the project that uses the clang++ compiler to build the my_project executable from the specified source files.

You can use these files to build and install your C++ project using CMake and Ninja. For example, you can run the following commands to build the project using CMake and Ninja:

# Create a build directory 
mkdir build 

# Generate the build files using CMake 
cd build 
cmake .. 

# Build the project using Ninja 
ninja 

# Install the project 
ninja install

This will build the my_project executable and install it to the bin directory. You can run the executable.

Thanks to ChatGPT from OpenAI.com for providing this tutorial. It may work, it may not.