使用Rust WASM接受类实例化函数的可选参数

如何解决使用Rust WASM接受类实例化函数的可选参数

我正在尝试从Rust严格的JavaScript中接收可选的字符串参数（请参见new函数）：

use regex::Regex;
use wasm_bindgen::prelude::*;

#[wasm_bindgen]
pub struct RustRegex {
  regex: Regex,}

#[wasm_bindgen]
impl RustRegex {
  #[wasm_bindgen(constructor)]
  pub fn new(pattern: String,flags: Option<String>) -> RustRegex {
    RustRegex {
      regex: Regex::new(&*format!(
        "(?{}:{})",flags.unwrap_or(String::from("")),pattern
      ))
      .unwrap(),}
  }

  pub fn test(&self,input: String) -> bool {
    return self.regex.is_match(&*input);
  }
}

但是，在尝试用wasm-pack build --target nodejs --dev进行编译后实例化该类时，出现此错误：

Welcome to Node.js v12.14.1.
Type ".help" for more information.
> const RustRegex = require("./pkg/hello_wasm").RustRegex
undefined
> new RustRegex("a","g")
Thrown:
RuntimeError: unreachable
    at __rust_start_panic (wasm-function[8363]:0x1dd97f)
    at rust_panic (wasm-function[7655]:0x1d8a82)
    at std::panicking::rust_panic_with_hook::hb2f1bd8b46640702 (wasm-function[1828]:0x150743)
    at rust_begin_unwind (wasm-function[6528]:0x1ca888)
    at core::panicking::panic_fmt::h3242de48a296a327 (wasm-function[7377]:0x1d5baa)
    at core::option::expect_none_failed::h3c7755bff09c9840 (wasm-function[3204]:0x186cb6)
    at core::result::Result<T,E>::unwrap::h2a78e2e00fb73d34 (wasm-function[1244]:0x12cbcb)
    at hello_wasm::RustRegex::new::h71a0ba83b340cb85 (wasm-function[407]:0xd41b6)
    at rustregex_new (wasm-function[755]:0x102da7)
    at new RustRegex (<redacted>\pkg\hello_wasm.js:72:24)
>

但是，我发现它仅在使用一个参数运行时有效，因此flags参数默认为空字符串：

Welcome to Node.js v12.14.1.
Type ".help" for more information.
> const RustRegex = require("./pkg/hello_wasm").RustRegex
undefined
> new RustRegex("a").test("a")
true
>

这使我可以将问题缩小到String参数的展开flags值。看起来在实例化过程中丢失了对它的某种引用，但是我不确定如何去做。也许解开的flags参数是不可复制的。重新分配变量似乎没有帮助，if let也没有帮助。我该如何解决？