rust 支持compile time的feature toggle，可以在 Cargo.toml 中指定feature

  1. [package]
  2. name = "feature_toggle"
  3. version = "0.1.0"
  4. authors = ["Sean <xujihui1985@gmail.com>"]
  5. edition = "2018"
  7. # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
  8. [dependencies]
  10. [features]
  11. benchmarking = []
  12. mutate_state = ["lazy_static"]
  13. enable_traceing = []
  14. enable_retry = []

key代表feature的名字，后面的[] 代表这个feature依赖的crate，例如 mutate_state 这个feature依赖 lazy_static，那么在打开这个feature后，cargo就会将lazy_static编译进来

通过annotation

  2. fn do_sth() {
  3.     println!("we do sth nornmal here");
  4.     #[cfg(feature="benchmarking")]
  5.     {
  6.         println!("benchmarking");
  7.         println!("we do sth inside benchmarking");
  8.     }
  9.     println!("we do sth after benchmarking");
  10. }
  13. fn main() {
  14.     do_sth();
  15. }

根据feature不同的实现

  1. #[derive(Debug)]
  2. struct MyStruct {
  3.     name: String,
  4. }
  6. #[cfg(feature="mutate_state")]
  7. fn mutate_slice(s: &mut [MyStruct]) {
  8.     println!("mutate_state");
  9.     for i in s.iter_mut() {
  10.         i.name = String::from("ddddd");
  11.     }
  12. }
  14. #[cfg(not(feature="mutate_state"))]
  15. fn mutate_slice(s: &mut [MyStruct]) {
  16.     println!("do not mutate state");
  17.     for i in s {
  18.         println!("{:?}", i);
  19.     }
  20. }
  22. fn main() {
  23.     let mut s = vec![
  24.         MyStruct{name: String::from("aaa")},
  25.         MyStruct{name: String::from("bbb")},
  26.         MyStruct{name: String::from("ccccc")},
  27.     ];
  28.     mutate_slice(&mut s);
  29.     for i in s.into_iter() {
  30.         println!("after mutate {:?}", i);
  31.     }
  32. }

compile time if expression

  1. fn complie_time_flag() {
  2.     if cfg!(feature="enable_traceing") {
  3.         println!("starting");
  4.     }
  5.     println!("in the body of complie_time_flag");
  6. }

compile time const

  1. #[cfg(feature="enable_retry")]
  2. const MAX_RETRY:u32 = 3;
  4. #[cfg(not(feature="enable_retry"))]
  5. const MAX_RETRY:u32 = 0;
  7. fn main() {
  8.     if cfg!(feature="enable_retry") {
  9.         println!("retry time {}", MAX_RETRY);
  10.     }
  11. }

build/run with feature

  1. cargo run --features "mutate_state","enable_traceing","enable_retry"