Rust Serde 为 Option：： 创建反序列化器

我有两个用于serde deserialize_with的定制函数

// Converts string to u32
pub fn de_u32_from_str<'de, D>(deserializer: D) -> Result<u32, D::Error>
where
    D: Deserializer<'de>,
{
    let s = String::deserialize(deserializer)?;
    s.parse::<u32>().map_err(de::Error::custom)
}

// Converts string that may be `null` to either `Some(u32)` or `None`
pub fn de_opt_u32_from_opt_str<'de, D>(deserializer: D) -> Result<Option<u32>, D::Error>
where
    D: Deserializer<'de>,
{
    let s = Option::<String>::deserialize(deserializer)?;
    s.map(|s| s.parse::<u32>().map_err(de::Error::custom))
        .transpose()
}

我测试了de_u32_from_str个这样的人:

fn deserialize_u32_from_str(string: &str, expected: u32) {
    let de: StrDeserializer<ValueError> = string.into_deserializer();
    let result = de_u32_from_str(de).unwrap();

    assert_eq!(result, expected);
}

然而，我很难为测试de_opt_u32_from_opt_str创建deserializer个

fn deserialize_opt_u32_from_opt_str(maybe_string: Option<&str>, expected: Option<u32>) {
    // I need a `deserializer` here
    let de: ... = ...;
    let result = de_opt_u32_from_opt_str(de).unwrap();

    assert_eq!(result, expected);
}

How can I create a deserializer like个

let de: StrDeserializer<ValueError> = string.into_deserializer();

but holding 100to satisfy

let s = Option::<String>::deserialize(deserializer)?;