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| -rw-r--r-- | src/doc/trpl/guessing-game.md | 21 |
1 files changed, 13 insertions, 8 deletions
diff --git a/src/doc/trpl/guessing-game.md b/src/doc/trpl/guessing-game.md index 431b7dc50a2..9f763e2fa13 100644 --- a/src/doc/trpl/guessing-game.md +++ b/src/doc/trpl/guessing-game.md @@ -410,11 +410,11 @@ $ cargo build Compiling guessing_game v0.1.0 (file:///home/you/projects/guessing_game) ``` -So, we told Cargo we wanted any version of `rand`, and so it fetched the -latest version at the time this was written, `v0.3.8`. But what happens -when next week, version `v0.4.0` comes out, which changes something with -`rand`, and it includes a breaking change? After all, a `v0.y.z` version -in SemVer can change every release. +So, we told Cargo we wanted any version of `rand`, and so it fetched the latest +version at the time this was written, `v0.3.8`. But what happens when next +week, version `v0.3.9` comes out, with an important bugfix? While getting +bugfixes is important, what if `0.3.9` contains a regression that breaks our +code? The answer to this problem is the `Cargo.lock` file you’ll now find in your project directory. When you build your project for the first time, Cargo @@ -422,12 +422,17 @@ figures out all of the versions that fit your criteria, and then writes them to the `Cargo.lock` file. When you build your project in the future, Cargo will see that the `Cargo.lock` file exists, and then use that specific version rather than do all the work of figuring out versions again. This lets you -have a repeatable build automatically. +have a repeatable build automatically. In other words, we’ll stay at `0.3.8` +until we explicitly upgrade, and so will anyone who we share our code with, +thanks to the lock file. -What about when we _do_ want to use `v0.4.0`? Cargo has another command, +What about when we _do_ want to use `v0.3.9`? Cargo has another command, `update`, which says ‘ignore the lock, figure out all the latest versions that fit what we’ve specified. If that works, write those versions out to the lock -file’. +file’. But, by default, Cargo will only look for versions larger than `0.3.0` +and smaller than `0.4.0`. If we want to move to `0.4.x`, we’d have to update +the `Cargo.toml` directly. When we do, the next time we `cargo build`, Cargo +will update the index and re-evaluate our `rand` requirements. There’s a lot more to say about [Cargo][doccargo] and [its ecosystem][doccratesio], but for now, that’s all we need to know. Cargo makes |