file_env_const

此crate提供在编译时从文件或环境变量加载数据并具有后备选项的宏。

当构建具有硬编码字符串的二进制文件时，你可能希望将其作为环境变量注入到构建环境中（例如在CI中），或者当离线构建时在本地文件中存储，两种情况都有后备选项。

示例

加载文件，具有环境后备

use file_env_const::file_env;
// Read data from file first
const FILE_DATA: &'static str = file_env!("Cargo.toml", "CARGO_PKG_NAME");
let f = std::fs::read_to_string("Cargo.toml").unwrap();
assert_eq!(FILE_DATA, f);

// Tries to read data from file, falls back to environment variable which is the package name
const FALL_BACK_TO_ENV: &'static str = file_env!("file_does_not_exist", "CARGO_PKG_NAME");
assert_eq!(FALL_BACK_TO_ENV, "file_env_const");

// Tries to read data from file, falls back to environment variable which is the package name
const FALL_BACK_TO_DEFAULT: &'static str =
    file_env!("file_does_not_exist", "ENV_NOT_FOUND", "fallback string");
assert_eq!(FALL_BACK_TO_DEFAULT, "fallback string");

加载环境变量，具有文件后备

use file_env_const::env_file;
// Read data from file first
const ENV_DATA: &'static str = env_file!("CARGO_PKG_NAME", "Cargo.toml");
assert_eq!(ENV_DATA, "file_env_const");

// Tries to read data from file, falls back to environment variable which is the package name
const FALL_BACK_TO_FILE: &'static str = env_file!("ENV_NOT_FOUND", "Cargo.toml");
let f = std::fs::read_to_string("Cargo.toml").unwrap();
assert_eq!(FALL_BACK_TO_FILE, f);

// Tries to read data from file, falls back to environment variable which is the package name
const FALL_BACK_TO_DEFAULT: &'static str =
    env_file!( "ENV_NOT_FOUND", "file_does_not_exist", "fallback string");
assert_eq!(FALL_BACK_TO_DEFAULT, "fallback string");