如何从num板条箱解析BigInt?

我正在尝试使用 BigInt 。我的代码如下:

extern crate num;
use num::bigint::BigInt;
...
println!("{}", from_str::<BigInt>("1")); //this is line 91 in the code

在我的货物中。toml文件我有以下内容:

[dependencies]
num = "0.1.30"

我的所作所为似乎与 this document , also this document 而且 an answer here on Stack Overflow .

然而,我得到了以下错误:

Compiling example v0.1.0 (file:///C:/src/rust/example)
src\main.rs:91:20: 91:38 error: unresolved name `from_str` [E0425]
src\main.rs:91     println!("{}", from_str::<BigInt>("1"));