json_map_serializer 0.1.3

Crate for easy serializing json maps from sequense of pairs
Documentation 
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use crate::{Error, Result};
use serde::ser::Impossible;
use serde::ser::Serialize;
use impl_serialize::impl_serialize;

pub struct MapKeySerializer;

impl serde::Serializer for MapKeySerializer {
    type Ok = String;
    type Error = Error;

    type SerializeSeq = Impossible<String, Error>;
    type SerializeTuple = Impossible<String, Error>;
    type SerializeTupleStruct = Impossible<String, Error>;
    type SerializeTupleVariant = Impossible<String, Error>;
    type SerializeMap = Impossible<String, Error>;
    type SerializeStruct = Impossible<String, Error>;
    type SerializeStructVariant = Impossible<String, Error>;

    #[inline]
    fn serialize_unit_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
    ) -> Result<String> {
        Ok(variant.to_owned())
    }

    #[inline]
    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<String>
    where
        T: ?Sized + Serialize,
    {
        value.serialize(self)
    }

    #[inline]
    fn serialize_char(self, value: char) -> Result<String> {
        Ok({
            let mut s = String::new();
            s.push(value);
            s
        })
    }

    #[inline]
    fn serialize_str(self, value: &str) -> Result<String> {
        Ok(value.to_owned())
    }

    fn collect_str<T>(self, value: &T) -> Result<String>
    where
        T: ?Sized + std::fmt::Display,
    {
        Ok(value.to_string())
    }

    impl_serialize!(Ok(v.to_string()), [
        i8, i16, i32, i64,
        u8, u16, u32, u64
    ]);

    impl_serialize!(Err(Error::KeyMustBeAString), [
        bool, f32, f64,
        bytes,
        unit, unit_struct,
        newtype_variant,
        none, some,
        seq, map,
        tuple, tuple_struct, tuple_variant,
        struct, struct_variant
    ]);
}

#[cfg(test)]
mod tests {
    use serde::Serialize;

    use super::*;

    #[test]
    fn str() {
        let input_str = "bar";
        
        let result = input_str.serialize(MapKeySerializer).unwrap();

        assert_eq!(result, String::from("bar"));
    }

    #[test]
    fn char() {
        let input_char = 'c';
        
        let result = input_char.serialize(MapKeySerializer).unwrap();

        assert_eq!(result, String::from("c"));
    }

    #[test]
    fn newtype_struct() {
        #[derive(Serialize)]
        struct NewType(char);

        let newtype_struct = NewType('g');

        let result = newtype_struct.serialize(MapKeySerializer).unwrap();

        assert_eq!(result, String::from("g"));
    }
}