1. rustup toolchain list
    2. 回车后，显示如下：
    3. C:\Users\Ur>rustup toolchain list
    4. stable-x86_64-pc-windows-gnu
    5. nightly-x86_64-pc-windows-gnu (default) /// 这个是当前使用中的
    1. rustup default stable/nightly/beta
    2. 注意，如果rustup default stable使用这样的命令，默认会安装stable-x86_64-pc-windows-msvc，所以如果是切换XXX-gnu，就要带上命名，如：
    3. rustup default stable-x86_64-pc-windows-gnu
    5. 几个安装和卸载的正确姿势：
    6. rustup toolchain install stable-x86_64-pc-windows-msvc
    7. rustup toolchain install nightly-x86_64-pc-windows-gnu
    9. rustup uninstall toolchain stable-x86_64-pc-windows-msvc
    10. rustup uninstall toolchain stable-x86_64-pc-windows-gnu
    1. rustup override set version
    2. 如：
    3. PS D:\workspace\rustwp> rustc -V
    4. rustc 1.40.0 (73528e339 2019-12-16)
    5. PS D:\workspace\rustwp> rustup override set nightly
    6. info: using existing install for 'nightly-x86_64-pc-windows-msvc'
    7. info: override toolchain for 'D:\workspace\rustwp' set to 'nightly-x86_64-pc-windows-msvc'
    9.   nightly-x86_64-pc-windows-msvc unchanged - rustc 1.42.0-nightly (6d3f4e0aa 2020-01-25)
    11. PS D:\workspace\rustwp> rustc -V
    12. rustc 1.42.0-nightly (6d3f4e0aa 2020-01-25)
    13. PS D:\workspace\rustwp>