ascii 1.1.0

ASCII-only equivalents to `char`, `str` and `String`.
Documentation 
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use std::fmt;

use serde::de::{Error, Unexpected, Visitor};
use serde::{Deserialize, Deserializer, Serialize, Serializer};

use ascii_char::AsciiChar;

impl Serialize for AsciiChar {
    #[inline]
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        serializer.serialize_char(self.as_char())
    }
}

struct AsciiCharVisitor;

impl<'de> Visitor<'de> for AsciiCharVisitor {
    type Value = AsciiChar;

    fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.write_str("an ascii character")
    }

    #[inline]
    fn visit_char<E: Error>(self, v: char) -> Result<Self::Value, E> {
        AsciiChar::from_ascii(v).map_err(|_| Error::invalid_value(Unexpected::Char(v), &self))
    }

    #[inline]
    fn visit_str<E: Error>(self, v: &str) -> Result<Self::Value, E> {
        if v.len() == 1 {
            let c = v.chars().next().unwrap();
            self.visit_char(c)
        } else {
            Err(Error::invalid_value(Unexpected::Str(v), &self))
        }
    }
}

impl<'de> Deserialize<'de> for AsciiChar {
    fn deserialize<D>(deserializer: D) -> Result<AsciiChar, D::Error>
    where
        D: Deserializer<'de>,
    {
        deserializer.deserialize_char(AsciiCharVisitor)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[cfg(feature = "serde_test")]
    const ASCII_CHAR: char = 'e';
    #[cfg(feature = "serde_test")]
    const ASCII_STR: &str = "e";
    #[cfg(feature = "serde_test")]
    const UNICODE_CHAR: char = 'é';

    #[test]
    fn basic() {
        fn assert_serialize<T: Serialize>() {}
        fn assert_deserialize<'de, T: Deserialize<'de>>() {}
        assert_serialize::<AsciiChar>();
        assert_deserialize::<AsciiChar>();
    }

    #[test]
    #[cfg(feature = "serde_test")]
    fn serialize() {
        use serde_test::{assert_tokens, Token};
        let ascii_char = AsciiChar::from_ascii(ASCII_CHAR).unwrap();
        assert_tokens(&ascii_char, &[Token::Char(ASCII_CHAR)]);
    }

    #[test]
    #[cfg(feature = "serde_test")]
    fn deserialize() {
        use serde_test::{assert_de_tokens, assert_de_tokens_error, Token};
        let ascii_char = AsciiChar::from_ascii(ASCII_CHAR).unwrap();
        assert_de_tokens(&ascii_char, &[Token::String(ASCII_STR)]);
        assert_de_tokens(&ascii_char, &[Token::Str(ASCII_STR)]);
        assert_de_tokens(&ascii_char, &[Token::BorrowedStr(ASCII_STR)]);
        assert_de_tokens_error::<AsciiChar>(
            &[Token::Char(UNICODE_CHAR)],
            "invalid value: character `é`, expected an ascii character",
        );
    }
}