Merge branch 'master' of https://github.com/limbo-rs/config-rs

6 files changed, 778 insertions, 57 deletions

diff --git a/src/config.rs b/src/config.rs
index 33d17bc..60f8551 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -3,11 +3,13 @@ use std::ops::Deref;
 use std::str::FromStr;
 use std::fmt::Debug;
 use serde::de::{Deserialize, Deserializer};
+use serde::ser::{Serialize, Serializer};
 
 use error::*;
 use source::Source;
+use ser::ConfigSerializer;
 
-use value::{Value, ValueWithKey};
+use value::{Value, ValueKind, ValueWithKey};
 use path;
 
 #[derive(Clone, Debug)]
@@ -190,6 +192,13 @@ impl Config {
         T::deserialize(self)
     }
 
+    /// Attempt to deserialize the entire configuration into the requested type.
+    pub fn try_from<T: Serialize>(from: &T) -> Result<Self> {
+        let mut serializer = ConfigSerializer::default();
+        from.serialize(&mut serializer)?;
+        Ok(serializer.output)
+    }
+
     #[deprecated(since="0.7.0", note="please use 'try_into' instead")]
     pub fn deserialize<'de, T: Deserialize<'de>>(self) -> Result<T> {
         self.try_into()
diff --git a/src/error.rs b/src/error.rs
index eff3c7c..56c827a 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -3,6 +3,7 @@ use std::borrow::Cow;
 use std::result;
 use std::fmt;
 use serde::de;
+use serde::ser;
 use nom;
 
 #[derive(Debug)]
@@ -201,3 +202,9 @@ impl de::Error for ConfigError {
         ConfigError::Message(msg.to_string())
     }
 }
+
+impl ser::Error for ConfigError {
+    fn custom<T: fmt::Display>(msg: T) -> Self {
+        ConfigError::Message(msg.to_string())
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 6178375..15e7672 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -26,6 +26,10 @@
 #[macro_use]
 extern crate serde;
 
+#[cfg(test)]
+#[macro_use]
+extern crate serde_derive;
+
 extern crate nom;
 
 #[macro_use]
@@ -46,6 +50,7 @@ extern crate serde_hjson;
 mod error;
 mod value;
 mod de;
+mod ser;
 mod path;
 mod source;
 mod config;
diff --git a/src/path/mod.rs b/src/path/mod.rs
index 258c4c4..f042992 100644
--- a/src/path/mod.rs
+++ b/src/path/mod.rs
@@ -58,77 +58,138 @@ impl Expression {
                 }
             }
 
-            Expression::Subscript(expr, index) => match expr.get(root) {
-                Some(value) => match value.kind {
-                    ValueKind::Array(ref array) => {
-                        let index = sindex_to_uindex(index, array.len());
-
-                        if index >= array.len() {
-                            None
-                        } else {
-                            Some(&array[index])
+            Expression::Subscript(expr, index) => {
+                match expr.get(root) {
+                    Some(value) => match value.kind {
+                        ValueKind::Array(ref array) => {
+                            let index = sindex_to_uindex(index, array.len());
+
+                            if index >= array.len() {
+                                None
+                            } else {
+                                Some(&array[index])
+                            }
                         }
-                    }
 
-                    _ => None,
-                },
+                        _ => None,
+                    },
 
-                _ => None,
+                    _ => None,
+                }
             },
         }
     }
 
     pub fn get_mut<'a>(&self, root: &'a mut Value) -> Option<&'a mut Value> {
         match *self {
-            Expression::Identifier(ref id) => match root.kind {
-                ValueKind::Table(ref mut map) => Some(
-                    map.entry(id.clone())
-                        .or_insert_with(|| Value::new(None, ValueKind::Nil)),
-                ),
+            Expression::Identifier(ref id) => {
+                match root.kind {
+                    ValueKind::Table(ref mut map) => map.get_mut(id),
 
-                _ => None,
+                    _ => None,
+                }
             },
 
-            Expression::Child(ref expr, ref key) => match expr.get_mut(root) {
-                Some(value) => match value.kind {
+            Expression::Child(ref expr, ref key) => {
+                match expr.get_mut(root) {
+                    Some(value) => {
+                        match value.kind {
+                            ValueKind::Table(ref mut map) => map.get_mut(key),
+
+                            _ => None
+                        }
+                    },
+
+                    _ => None,
+                }
+            },
+
+            Expression::Subscript(ref expr, index) => {
+                match expr.get_mut(root) {
+                    Some(value) => match value.kind {
+                        ValueKind::Array(ref mut array) => {
+                            let index = sindex_to_uindex(index, array.len());
+
+                            if index >= array.len() {
+                                None
+                            } else {
+                                Some(&mut array[index])
+                            }
+                        }
+
+                        _ => None,
+                    },
+
+                    _ => None,
+                }
+            },
+        }
+    }
+
+    pub fn get_mut_forcibly<'a>(&self, root: &'a mut Value) -> Option<&'a mut Value> {
+        match *self {
+            Expression::Identifier(ref id) => {
+                match root.kind {
                     ValueKind::Table(ref mut map) => Some(
-                        map.entry(key.clone())
+                        map.entry(id.clone())
                             .or_insert_with(|| Value::new(None, ValueKind::Nil)),
                     ),
 
-                    _ => {
-                        *value = HashMap::<String, Value>::new().into();
+                    _ => None,
+                }
+            },
 
-                        if let ValueKind::Table(ref mut map) = value.kind {
-                            Some(
-                                map.entry(key.clone())
-                                    .or_insert_with(|| Value::new(None, ValueKind::Nil)),
-                            )
-                        } else {
-                            unreachable!();
+            Expression::Child(ref expr, ref key) => {
+                match expr.get_mut_forcibly(root) {
+                    Some(value) => match value.kind {
+                        ValueKind::Table(ref mut map) => Some(
+                            map.entry(key.clone())
+                                .or_insert_with(|| Value::new(None, ValueKind::Nil)),
+                        ),
+
+                        _ => {
+                            *value = HashMap::<String, Value>::new().into();
+
+                            if let ValueKind::Table(ref mut map) = value.kind {
+                                Some(
+                                    map.entry(key.clone())
+                                        .or_insert_with(|| Value::new(None, ValueKind::Nil)),
+                                )
+                            } else {
+                                unreachable!();
+                            }
                         }
-                    }
-                },
+                    },
 
-                _ => None,
+                    _ => None,
+                }
             },
 
-            Expression::Subscript(ref expr, index) => match expr.get_mut(root) {
-                Some(value) => match value.kind {
-                    ValueKind::Array(ref mut array) => {
-                        let index = sindex_to_uindex(index, array.len());
-
-                        if index >= array.len() {
-                            array.resize((index + 1) as usize, Value::new(None, ValueKind::Nil));
+            Expression::Subscript(ref expr, index) => {
+                let mut do_again = false;
+                match expr.get_mut_forcibly(root) {
+                    Some(value) => {
+                        match value.kind {
+                            ValueKind::Array(_) => (),
+                            _ => *value = Vec::<Value>::new().into()
                         }
 
-                        Some(&mut array[index])
-                    }
+                        match value.kind {
+                            ValueKind::Array(ref mut array) => {
+                                let index = sindex_to_uindex(index, array.len());
 
-                    _ => None,
-                },
+                                if index >= array.len() {
+                                    array.resize((index + 1) as usize, Value::new(None, ValueKind::Nil));
+                                }
+
+                                Some(&mut array[index])
+                            }
 
-                _ => None,
+                            _ => None
+                        }
+                    },
+                    _ => None
+                }
             },
         }
     }
@@ -171,7 +232,7 @@ impl Expression {
             }
 
             Expression::Child(ref expr, ref key) => {
-                if let Some(parent) = expr.get_mut(root) {
+                if let Some(parent) = expr.get_mut_forcibly(root) {
                     match parent.kind {
                         ValueKind::Table(_) => {
                             Expression::Identifier(key.clone()).set(parent, value);
@@ -188,11 +249,15 @@ impl Expression {
             }
 
             Expression::Subscript(ref expr, index) => {
-                if let Some(parent) = expr.get_mut(root) {
+                if let Some(parent) = expr.get_mut_forcibly(root) {
+                    match parent.kind {
+                        ValueKind::Array(_) => (),
+                        _ => *parent = Vec::<Value>::new().into()
+                    }
+
                     match parent.kind {
                         ValueKind::Array(ref mut array) => {
                             let uindex = sindex_to_uindex(index, array.len());
-
                             if uindex >= array.len() {
                                 array.resize(
                                     (uindex + 1) as usize,
@@ -203,13 +268,7 @@ impl Expression {
                             array[uindex] = value.clone();
                         }
 
-                        _ => {
-                            // Didn't find an array ...
-                            // Add an array and do this again
-                            *parent = Vec::<Value>::new().into();
-
-                            Expression::Subscript(expr.clone(), index).set(parent, value);
-                        }
+                        _ => ()
                     }
                 }
             }
diff --git a/src/path/parser.rs b/src/path/parser.rs
index 7629193..3ec433e 100644
--- a/src/path/parser.rs
+++ b/src/path/parser.rs
@@ -101,6 +101,15 @@ mod test {
         let expected = Child(Box::new(Identifier("abcd".into())), "efgh".into());
 
         assert_eq!(parsed, expected);
+
+        let parsed: Expression = from_str("abcd.efgh.ijkl").unwrap();
+        let expected = Child(Box::new(
+            Child(Box::new(
+                Identifier("abcd".into())
+            ), "efgh".into())
+        ), "ijkl".into());
+
+        assert_eq!(parsed, expected);
     }
 
     #[test]
diff --git a/src/ser.rs b/src/ser.rs
new file mode 100644
index 0000000..0366472
--- /dev/null
+++ b/src/ser.rs
@@ -0,0 +1,632 @@
+use std::mem;
+use std::fmt::Display;
+use serde::ser;
+
+use Config;
+use value::{Value, ValueKind, ValueWithKey};
+use error::*;
+
+#[derive(Default, Debug)]
+pub struct ConfigSerializer {
+    keys: Vec<(String, Option<usize>)>,
+    pub output: Config,
+}
+
+impl ConfigSerializer {
+    fn serialize_primitive<T>(&mut self, value: T) -> Result<()>
+        where T: Into<Value> + Display
+    {
+        let key = match self.last_key_index_pair() {
+            Some((key, Some(index))) => format!("{}[{}]", key, index),
+            Some((key, None)) => key.to_string(),
+            None => return Err(ConfigError::Message(format!("key is not found for value {}", value)))
+        };
+        self.output.set(&key, value.into())?;
+        Ok(())
+    }
+
+    fn last_key_index_pair(&self) -> Option<(&str, Option<usize>)> {
+        let len = self.keys.len();
+        if len > 0 {
+            self.keys.get(len - 1)
+                .map(|&(ref key, opt)| (key.as_str(), opt))
+        } else {
+            None
+        }
+    }
+
+    fn inc_last_key_index(&mut self) -> Result<()> {
+        let len = self.keys.len();
+        if len > 0 {
+            self.keys.get_mut(len - 1)
+                .map(|pair| {
+                    pair.1 = pair.1.map(|i| i + 1).or(Some(0))
+                })
+                .ok_or(ConfigError::Message(
+                    format!("last key is not found in {} keys", len)
+                ))
+        } else {
+            Err(ConfigError::Message("keys is empty".to_string()))
+        }
+    }
+
+    fn make_full_key(&self, key: &str) -> String {
+        let len = self.keys.len();
+        if len > 0 {
+            if let Some(&(ref prev_key, index)) = self.keys.get(len - 1) {
+                return if let Some(index) = index {
+                    format!("{}[{}].{}", prev_key, index, key)
+                } else {
+                    format!("{}.{}", prev_key, key)
+                }
+            }
+        }
+        key.to_string()
+    }
+
+    fn push_key(&mut self, key: &str) {
+        let full_key = self.make_full_key(key);
+        self.keys.push((full_key, None));
+    }
+
+    fn pop_key(&mut self) -> Option<(String, Option<usize>)> {
+        self.keys.pop()
+    }
+}
+
+impl<'a> ser::Serializer for &'a mut ConfigSerializer {
+    type Ok = ();
+    type Error = ConfigError;
+    type SerializeSeq = Self;
+    type SerializeTuple = Self;
+    type SerializeTupleStruct = Self;
+    type SerializeTupleVariant = Self;
+    type SerializeMap = Self;
+    type SerializeStruct = Self;
+    type SerializeStructVariant = Self;
+
+    fn serialize_bool(self, v: bool) -> Result<Self::Ok> {
+        self.serialize_primitive(v)
+    }
+
+    fn serialize_i8(self, v: i8) -> Result<Self::Ok> {
+        self.serialize_i64(v as i64)
+    }
+
+    fn serialize_i16(self, v: i16) -> Result<Self::Ok> {
+        self.serialize_i64(v as i64)
+    }
+
+    fn serialize_i32(self, v: i32) -> Result<Self::Ok> {
+        self.serialize_i64(v as i64)
+    }
+
+    fn serialize_i64(self, v: i64) -> Result<Self::Ok> {
+        self.serialize_primitive(v)
+    }
+
+    fn serialize_u8(self, v: u8) -> Result<Self::Ok> {
+        self.serialize_u64(v as u64)
+    }
+
+    fn serialize_u16(self, v: u16) -> Result<Self::Ok> {
+        self.serialize_u64(v as u64)
+    }
+
+    fn serialize_u32(self, v: u32) -> Result<Self::Ok> {
+        self.serialize_u64(v as u64)
+    }
+
+    fn serialize_u64(self, v: u64) -> Result<Self::Ok> {
+        if v > (i64::max_value() as u64) {
+            Err(ConfigError::Message(
+                format!("value {} is greater than the max {}", v, i64::max_value())
+            ))
+        } else {
+            self.serialize_i64(v as i64)
+        }
+    }
+
+    fn serialize_f32(self, v: f32) -> Result<Self::Ok> {
+        self.serialize_f64(v as f64)
+    }
+
+    fn serialize_f64(self, v: f64) -> Result<Self::Ok> {
+        self.serialize_primitive(v)
+    }
+
+    fn serialize_char(self, v: char) -> Result<Self::Ok> {
+        self.serialize_primitive(v.to_string())
+    }
+
+    fn serialize_str(self, v: &str) -> Result<Self::Ok> {
+        self.serialize_primitive(v.to_string())
+    }
+
+    fn serialize_bytes(self, v: &[u8]) -> Result<Self::Ok> {
+        use serde::ser::SerializeSeq;
+        let mut seq = self.serialize_seq(Some(v.len()))?;
+        for byte in v {
+            seq.serialize_element(byte)?;
+        }
+        seq.end()
+    }
+
+    fn serialize_none(self) -> Result<Self::Ok> {
+        self.serialize_unit()
+    }
+
+    fn serialize_some<T>(self, value: &T) -> Result<Self::Ok>
+        where T: ?Sized + ser::Serialize
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_unit(self) -> Result<Self::Ok> {
+        self.serialize_primitive(Value::from(ValueKind::Nil))
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<Self::Ok> {
+        self.serialize_unit()
+    }
+
+    fn serialize_unit_variant(self, _name: &'static str, _variant_index: u32, variant: &'static str)
+        -> Result<Self::Ok>
+    {
+        self.serialize_str(&variant.to_lowercase())
+    }
+
+    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<Self::Ok>
+        where T: ?Sized + ser::Serialize
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T>(self, _name: &'static str, _variant_index: u32, variant: &'static str, value: &T)
+        -> Result<Self::Ok>
+        where T: ?Sized + ser::Serialize
+    {
+        self.push_key(&variant.to_lowercase());
+        value.serialize(&mut *self)?;
+        self.pop_key();
+        Ok(())
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Ok(self)
+    }
+
+    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_struct(self, _name: &'static str, len: usize)
+        -> Result<Self::SerializeTupleStruct>
+    {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_variant(self, name: &'static str, _variant_index: u32, variant: &'static str, _len: usize)
+        -> Result<Self::SerializeTupleVariant>
+    {
+        self.push_key(&variant.to_lowercase());
+        Ok(self)
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Ok(self)
+    }
+
+    fn serialize_struct(self, _name: &'static str, len: usize) -> Result<Self::SerializeStruct> {
+        self.serialize_map(Some(len))
+    }
+
+    fn serialize_struct_variant(self, _name: &'static str, _variant_index: u32, variant: &'static str, len: usize)
+        -> Result<Self::SerializeStructVariant>
+    {
+        self.push_key(&variant.to_lowercase());
+        Ok(self)
+    }
+}
+
+impl<'a> ser::SerializeSeq for &'a mut ConfigSerializer {
+    type Ok = ();
+    type Error = ConfigError;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        self.inc_last_key_index()?;
+        value.serialize(&mut **self)?;
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        Ok(())
+    }
+}
+
+impl<'a> ser::SerializeTuple for &'a mut ConfigSerializer {
+    type Ok = ();
+    type Error = ConfigError;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        self.inc_last_key_index()?;
+        value.serialize(&mut **self)?;
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        Ok(())
+    }
+}
+
+impl<'a> ser::SerializeTupleStruct for &'a mut ConfigSerializer {
+    type Ok = ();
+    type Error = ConfigError;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        self.inc_last_key_index()?;
+        value.serialize(&mut **self)?;
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        Ok(())
+    }
+}
+
+impl<'a> ser::SerializeTupleVariant for &'a mut ConfigSerializer {
+    type Ok = ();
+    type Error = ConfigError;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        self.inc_last_key_index()?;
+        value.serialize(&mut **self)?;
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        self.pop_key();
+        Ok(())
+    }
+}
+
+impl<'a> ser::SerializeMap for &'a mut ConfigSerializer {
+    type Ok = ();
+    type Error = ConfigError;
+
+    fn serialize_key<T>(&mut self, key: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        let key_serializer = StringKeySerializer;
+        let key = key.serialize(key_serializer)?;
+        self.push_key(&key);
+        Ok(())
+    }
+
+    fn serialize_value<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        value.serialize(&mut **self)?;
+        self.pop_key();
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        Ok(())
+    }
+}
+
+impl<'a> ser::SerializeStruct for &'a mut ConfigSerializer {
+    type Ok = ();
+    type Error = ConfigError;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        self.push_key(key);
+        value.serialize(&mut **self)?;
+        self.pop_key();
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        Ok(())
+    }
+}
+
+impl<'a> ser::SerializeStructVariant for &'a mut ConfigSerializer {
+    type Ok = ();
+    type Error = ConfigError;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        self.push_key(key);
+        value.serialize(&mut **self)?;
+        self.pop_key();
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        self.pop_key();
+        Ok(())
+    }
+}
+
+pub struct StringKeySerializer;
+
+impl ser::Serializer for StringKeySerializer {
+    type Ok = String;
+    type Error = ConfigError;
+    type SerializeSeq = Self;
+    type SerializeTuple = Self;
+    type SerializeTupleStruct = Self;
+    type SerializeTupleVariant = Self;
+    type SerializeMap = Self;
+    type SerializeStruct = Self;
+    type SerializeStructVariant = Self;
+
+    fn serialize_bool(self, v: bool) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_i8(self, v: i8) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_i16(self, v: i16) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_i32(self, v: i32) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_i64(self, v: i64) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_u8(self, v: u8) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_u16(self, v: u16) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_u32(self, v: u32) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_u64(self, v: u64) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_f32(self, v: f32) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_f64(self, v: f64) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_char(self, v: char) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_str(self, v: &str) -> Result<Self::Ok> {
+        Ok(v.to_string())
+    }
+
+    fn serialize_bytes(self, v: &[u8]) -> Result<Self::Ok> {
+        Ok(String::from_utf8_lossy(v).to_string())
+    }
+
+    fn serialize_none(self) -> Result<Self::Ok> {
+        self.serialize_unit()
+    }
+
+    fn serialize_some<T>(self, value: &T) -> Result<Self::Ok>
+        where T: ?Sized + ser::Serialize
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_unit(self) -> Result<Self::Ok> {
+        Ok(String::new())
+    }
+
+    fn serialize_unit_struct(self, _name: &str) -> Result<Self::Ok> {
+        self.serialize_unit()
+    }
+
+    fn serialize_unit_variant(self, _name: &str, _variant_index: u32, variant: &str) -> Result<Self::Ok> {
+        Ok(variant.to_lowercase())
+    }
+
+    fn serialize_newtype_struct<T>(self, _name: &str, value: &T) -> Result<Self::Ok>
+        where T: ?Sized + ser::Serialize
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T>(self, _name: &str, _variant_index: u32, _variant: &str, value: &T)
+        -> Result<Self::Ok>
+        where T: ?Sized + ser::Serialize
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Err(ConfigError::Message("seq can't serialize to string key".to_string()))
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
+        Err(ConfigError::Message("tuple can't serialize to string key".to_string()))
+    }
+
+    fn serialize_tuple_struct(self, name: &str, _len: usize) -> Result<Self::SerializeTupleStruct> {
+        Err(ConfigError::Message(format!("tuple struct {} can't serialize to string key", name)))
+    }
+
+    fn serialize_tuple_variant(self, name: &str, _variant_index: u32, variant: &str, _len: usize)
+        -> Result<Self::SerializeTupleVariant>
+    {
+        Err(ConfigError::Message(format!("tuple variant {}::{} can't serialize to string key", name, variant)))
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Err(ConfigError::Message("map can't serialize to string key".to_string()))
+    }
+
+    fn serialize_struct(self, name: &str, _len: usize) -> Result<Self::SerializeStruct> {
+        Err(ConfigError::Message(format!("struct {} can't serialize to string key", name)))
+    }
+
+    fn serialize_struct_variant(self, name: &str, _variant_index: u32, variant: &str, _len: usize)
+        -> Result<Self::SerializeStructVariant>
+    {
+        Err(ConfigError::Message(format!("struct variant {}::{} can't serialize to string key", name, variant)))
+    }
+}
+
+
+impl ser::SerializeSeq for StringKeySerializer {
+    type Ok = String;
+    type Error = ConfigError;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        unreachable!()
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        unreachable!()
+    }
+}
+
+impl ser::SerializeTuple for StringKeySerializer {
+    type Ok = String;
+    type Error = ConfigError;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        unreachable!()
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        unreachable!()
+    }
+}
+
+impl ser::SerializeTupleStruct for StringKeySerializer {
+    type Ok = String;
+    type Error = ConfigError;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        unreachable!()
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        unreachable!()
+    }
+}
+
+impl ser::SerializeTupleVariant for StringKeySerializer {
+    type Ok = String;
+    type Error = ConfigError;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        unreachable!()
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        unreachable!()
+    }
+}
+
+impl ser::SerializeMap for StringKeySerializer {
+    type Ok = String;
+    type Error = ConfigError;
+
+    fn serialize_key<T>(&mut self, key: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        unreachable!()
+    }
+
+    fn serialize_value<T>(&mut self, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        unreachable!()
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        unreachable!()
+    }
+}
+
+impl ser::SerializeStruct for StringKeySerializer {
+    type Ok = String;
+    type Error = ConfigError;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        unreachable!()
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        unreachable!()
+    }
+}
+
+impl ser::SerializeStructVariant for StringKeySerializer {
+    type Ok = String;
+    type Error = ConfigError;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+        where T: ?Sized + ser::Serialize
+    {
+        unreachable!()
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        unreachable!()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use serde::Serialize;
+
+    #[test]
+    fn test_struct() {
+        #[derive(Debug, Serialize, Deserialize, PartialEq)]
+        struct Test {
+            int: u32,
+            seq: Vec<String>,
+        }
+
+        let test = Test { int: 1, seq: vec!["a".to_string(), "b".to_string()] };
+        let config = Config::try_from(&test).unwrap();
+
+        let actual: Test = config.try_into().unwrap();
+        assert_eq!(test, actual);
+    }
+}