未能为要求选择一个版本`rand ='^0.9.0;

Question

我每次运行货物构建：

error: failed to select a version for the requirement `rand = "^0.9.0"`
candidate versions found which didn't match: 0.8.5, 0.8.4, 0.8.3, ...
location searched: crates.io index
required by package `guessing_game v0.1.0 (D:\Adwait\Rust\project\guessing_game)`

cargo.toml看起来像这样的错误，我会遇到此错误。

[package]
name = "guessing_game"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
rand = "0.9.0"

Answer 1

由于没有版本0.9.0可用，因此引起了此错误。将其更新为0.8.0。货物toml应该看起来像这样。

[package]
name = "guessing_game"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
rand = "0.8.0"

Answer 2

我自己经历了这个，我相信这种混乱是源于关于Rust的教程提及0.9.0作为了解升级锈蚀箱的一个例子。

我不确定他们为什么选择这个例子，因为它不存在。如果您是Rust的新手，并且想使用升级的Rust Crate，则可以将0.7.x升级到0.8.0是一个更好的主意。

Answer 3

遇到这样的错误的另一个可能原因是，您的编译器已过时，新版本的库针对新编译器。使用Rustup Update更新工具链。

我有一个使用拍手4.2的项目，但拒绝在另一台计算机上编译，其中有这样的错误。

Answer 4

我只是一个初学者学习Rust的人，但是从我所看到的，如果您使用货物搜索rand您获得了此输出：

username@PC:~/Projects/guessing_game$ cargo search rand
rand = "0.9.0-beta.1"        # Random number generators and other randomness functionality. 
bevy_rand = "0.8.0"          # A plugin to integrate rand for ECS optimised RNG for the Bevy game engine.
tinyrand = "0.5.0"           # Lightweight RNG specification and several ultrafast implementations in Rust.
rand-construct = "0.10.0"    # Encapsulates the random-constructible and random-constructible-derive crates which are used for cr…
random_derive = "0.0.0"      # Procedurally defined macro for automatically deriving rand::Rand for structs and enums
tera-rand = "0.2.0"          # A suite of random data generation functions for the Tera template engine
tera-rand-cli = "0.2.0"      # A CLI tool for generating a feed of random data from a Tera template
rands = "0.8.8"              # Random number generators and other randomness functionality. 
faker_rand = "0.1.1"         # Fake data generators for lorem ipsum, names, emails, and more
rand_derive2 = "0.1.21"      # Generate customizable random types with the rand crate
... and 1581 crates more (use --limit N to see more)
note: to learn more about a package, run `cargo info <name>`

如您所见，“ 0.9.0”是Beta版本，这就是为什么它会给您错误。如果您仍然想使用它，则可以在cargo.toml文件中编写rand = {version =“ 0.9.0-beta.1”}。

如果您只想最新的稳定版本RAND（或任何其他依赖关系，从我到现在为止），则可以使用货物添加rand，它将自动添加“ 0.8.5”货物文件的版本。

如果出于某种原因，您想手动添加它们，则可以使用货物信息rand，这将为您提供此输出：

username@PC:~/Projects/guessing_game$ cargo info rand
rand #random #rng
Random number generators and other randomness functionality.
version: 0.8.5 (latest 0.9.0-beta.1)
license: MIT OR Apache-2.0
rust-version: unknown
documentation: https://docs.rs/rand
homepage: https://rust-random.github.io/book
repository: https://github.com/rust-random/rand
crates.io: https://crates.io/crates/rand/0.8.5
features:
 +default       = [std, std_rng]
  alloc         = [rand_core/alloc]
  getrandom     = [rand_core/getrandom]
  libc          = [dep:libc]
  rand_chacha   = [dep:rand_chacha]
  std           = [rand_core/std, rand_chacha/std, alloc, getrandom, libc]
  std_rng       = [rand_chacha]
  log           = [dep:log]
  min_const_gen = []
  nightly       = []
  packed_simd   = [dep:packed_simd]
  serde         = [dep:serde]
  serde1        = [serde, rand_core/serde1]
  simd_support  = [packed_simd]
  small_rng     = []
note: to see how you depend on rand, run `cargo tree --invert --package [email protected]`

然后，您可以将输出中看到的版本添加到cargo.toml文件。