lazy_static的延迟初始化？-解网

问：

我已经在以下方面取得了一些成功：lazy_static

static ref WORD_COUNT_REPORTING_STEP_MUTEX: Arc<Mutex<usize>> = Arc::new(Mutex::new(0));
static ref INDEX_NAME: RwLock<String> = RwLock::new("".to_string());
static ref LANGUAGE_DETECTOR: LanguageDetector = LanguageDetectorBuilder::from_all_languages().with_preloaded_language_models().build();

但是我真的在为看似相当简单的模式挠头：将某种类型设置为，然后在发现确实是 .如果发现是，则跳过初始化。在初始化块之后，获取和。Option<T>NoneOptionNoneOptionSomeOptionunwrap()

注意，这里的类型是 .reqwest::blocking::client::Client

到目前为止，我有：

lazy_static! {
    static ref REQWEST_CLIENT_OPTION: Option<Client> = None;
}

然后，在一个函数中：

...
match &*REQWEST_CLIENT_OPTION {
    Some(reqwest_client) => {
        info!("reqwest_client_option currently non-None");
    },
    None => {
        info!("reqwest_client_option currently None");
        
        // configuration and build of the client
        let es_path = r#"D:\apps\ElasticSearch\elasticsearch-8.6.2\config"#;
        set_var("ES_PATH_CONF", &es_path); // from crate tmp_env
        let mut buf = Vec::new();
        let cert_path = format!(r#"{es_path}\certs\http_ca.crt"#);
        let mut cert_file = File::open(cert_path).expect("problem opening certificate file");
        cert_file.read_to_end(&mut buf).ok();
        let cert = reqwest::Certificate::from_pem(&buf).expect("problem generating certificate"); // delivers cert OK
        let reqwest_client = Client::builder()
            .add_root_certificate(cert)
            .timeout(std::time::Duration::from_millis(5_000))
            .build().expect("problem building the request client");

        // now I try to set the Option...
        let mut static_client = &*REQWEST_CLIENT_OPTION;
        info!("static_client type {}", utilities::str_type_of(&static_client));
        // static_client type &core::option::Option<reqwest::blocking::client::Client>
        static_client = &Some(reqwest_client)
        // not now possible to check static_client. 
    }
}
let reqwest_client = REQWEST_CLIENT_OPTION.as_ref().unwrap();    
...

以上主要是猜测。毋庸置疑，我已经尝试了无数次涉及 *、& 和类似 .我希望这可能会起作用：let_mut

*static_client = Some(reqwest_client);

...但这失败了：“ ^^^^^^^^^^^^^^ 是一个参考，所以它引用的数据不能写入”。static_client&

至少上面的代码编译正常。
打印“reqwest_client_option当前无”行。
但令我失望的是，最后一行引起了恐慌：

pyo3_runtime.PanicException: called `Option::unwrap()` on a `None` value

注意：我也尝试了一个变体，但遇到了同样的问题。这种结构可能会更优雅。if let Some(reqwest_client) ...

锈选项类型 lazy-initialization 惰性静态

use std::sync::OnceLock;
use reqwest::blocking::Client;

static REQWEST_CLIENT: OnceLock<Client> = OnceLock::new();

fn main(){
    let client = REQWEST_CLIENT.get_or_init(|| {
        Client::builder()
            // other options
            .build()
            .expect("problem building the reqwest client")
    });

    // use client
}

lazy_static的延迟初始化？

Lazy initialisation of lazy_static?

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