rustup 可以幫助我們安裝不同版本的rust 編程需要的工具連，同時可以方便的進行不同版本
之間的切換，類似nodejs 的nvm,n, ruby 的 rvm python 的 venv 。。。
rustup 基本使用
我們在首次使用安裝腳本，或者安裝包安裝完成rust 之后就會附帶rustup了，對於需要使用不同版本
的流程如下：
- 選擇一個版本，rust 提供了不同的channnel(nightly,stabel,beta. date 格式..)
- 使用
rustup install指定版本，或者rustup toolchain install - 指定
rustup default version進行版本切換 - 使用
rustup toolchain list或者rustup show檢查切換配置
rustup 幫助
- toolchain
rustup-toolchain
Modify or query the installed toolchains
USAGE:
rustup toolchain <SUBCOMMAND>
FLAGS:
-h, --help Prints help information
SUBCOMMANDS:
list List installed toolchains
install Install or update a given toolchain
uninstall Uninstall a toolchain
link Create a custom toolchain by symlinking to a directory
help Prints this message or the help of the given subcommand(s)
DISCUSSION:
Many `rustup` commands deal with *toolchains*, a single
installation of the Rust compiler. `rustup` supports multiple
types of toolchains. The most basic track the official release
channels: 'stable', 'beta' and 'nightly'; but `rustup` can also
install toolchains from the official archives, for alternate host
platforms, and from local builds.
Standard release channel toolchain names have the following form:
<channel>[-<date>][-<host>]
<channel> = stable|beta|nightly|<version>
<date> = YYYY-MM-DD
<host> = <target-triple>
'channel' is either a named release channel or an explicit version
number, such as '1.8.0'. Channel names can be optionally appended
with an archive date, as in 'nightly-2017-05-09', in which case
the toolchain is downloaded from the archive for that date.
Finally, the host may be specified as a target triple. This is
most useful for installing a 32-bit compiler on a 64-bit platform,
or for installing the [MSVC-based toolchain] on Windows. For
example:
$ rustup toolchain install stable-x86_64-pc-windows-msvc
For convenience, elements of the target triple that are omitted
will be inferred, so the above could be written:
$ rustup default stable-msvc
rustup can also manage symlinked local toolchain builds, which are
often used to for developing Rust itself. For more information see
`rustup toolchain help link`.
一個簡單安裝例子
比如我們需要安裝一個nightly-2019-01-17 , 這個格式遵循上邊的約定
- 安裝如下：
rustup toolchain install nightly-2019-01-17
信息如下：
可以看出信息還是很詳細的（我們同時也知道了版本）
rustup toolchain install nightly-2019-01-17
info: syncing channel updates for 'nightly-2019-01-17-x86_64-apple-darwin'
316.6 KiB / 316.6 KiB (100 %) 223.0 KiB/s in 1s ETA: 0s
info: latest update on 2019-01-17, rust version 1.33.0-nightly (ceb251214 2019-01-16)
info: downloading component 'rustc'
78.6 MiB / 78.6 MiB (100 %) 537.6 KiB/s in 3m 6s ETA: 0s
info: downloading component 'rust-std'
48.0 MiB / 51.3 MiB ( 94 %) 44.8 KiB/s in 3m 14s ETA: 1m 15s
48.0 MiB / 51.3 MiB ( 94 %) 48.0 KiB/s in 3m 16s ETA: 1m 8s
51.3 MiB / 51.3 MiB (100 %) 282.4 KiB/s in 3m 36s ETA: 0s
info: downloading component 'cargo'
3.4 MiB / 3.4 MiB (100 %) 388.1 KiB/s in 9s ETA: 0s
info: downloading component 'rust-docs'
8.5 MiB / 8.5 MiB (100 %) 606.9 KiB/s in 18s ETA: 0s
info: installing component 'rustc'
78.6 MiB / 78.6 MiB (100 %) 8.9 MiB/s in 7s ETA: 0s
info: installing component 'rust-std'
51.3 MiB / 51.3 MiB (100 %) 12.1 MiB/s in 4s ETA: 0s
info: installing component 'cargo'
info: installing component 'rust-docs'
8.5 MiB / 8.5 MiB (100 %) 1.3 MiB/s in 6s ETA: 0s
nightly-2019-01-17-x86_64-apple-darwin installed - rustc 1.33.0-nightly (ceb251214 2019-01-16)
info: checking for self-updates
- 啟動新的為default
rustup default nightly-2019-01-17
- 查看toolchain
rustup toolchain list
效果：
stable-x86_64-apple-darwin
nightly-2019-01-17-x86_64-apple-darwin (default)
nightly-x86_64-apple-darwin
- 配置default
我們可以使用
<channel>[-<date>][-<host>]格式，也可以使用 toolchain list 看到的版本
rustup default nightly-2019-01-17
效果
info: using existing install for 'nightly-2019-01-17-x86_64-apple-darwin'
info: default toolchain set to 'nightly-2019-01-17-x86_64-apple-darwin'
nightly-2019-01-17-x86_64-apple-darwin unchanged - rustc 1.33.0-nightly (ceb251214 2019-01-16)
- 檢查default
rustup show
效果：
Default host: x86_64-apple-darwin
installed toolchains
--------------------
stable-x86_64-apple-darwin
nightly-2019-01-17-x86_64-apple-darwin (default)
nightly-x86_64-apple-darwin
active toolchain
----------------
nightly-2019-01-17-x86_64-apple-darwin (default)
rustc 1.33.0-nightly (ceb251214 2019-01-16)
或者：
rustup toolchain list
效果：
stable-x86_64-apple-darwin
nightly-2019-01-17-x86_64-apple-darwin (default)
nightly-x86_64-apple-darwin
說明
因為rust 語言的變動，可能經常碰到編譯問題（依賴別人的包），通過rustup 的版本管理，基本上可以解決我們
實際碰到的問題，同時對於不同版本包的問題，可以結合github 的issue 進行查看（好多時候都會找到的）
參考資料
https://forge.rust-lang.org/channel-layout.html
https://forge.rust-lang.org/
https://forge.rust-lang.org/releases.html
https://rust-lang.github.io/rustup-components-history/index.html