fix for issue #60

src/config.rs

@@ -11,6 +11,7 @@ use source::Source;
 
 use path;
 use value::{Value, ValueKind, ValueWithKey};
+use file::{File, FileFormat};
 
 #[derive(Clone, Debug)]
 enum ConfigKind {
@@ -49,7 +50,10 @@ pub struct Config {
 
 impl Config {
     pub fn new() -> Self {
-        Config::default()
+        let mut c = Config::default();
+        c.merge(File::from_str("", FileFormat::Toml));
+
+        c
     }
 
     /// Merge in a configuration property source.
@@ -129,6 +133,25 @@ impl Config {
         self.refresh()
     }
 
+    pub fn set_defaults<T: Serialize + Default>(&mut self, value: T) -> Result<&mut Config>
+    {
+        match self.kind{
+            ConfigKind::Mutable {
+                ref mut defaults, ..
+            } => {
+                let mut serializer = ConfigSerializer::default();
+                value.serialize(&mut serializer)?;
+                for (key, val) in serializer.output.collect()?{
+                    defaults.insert(key.parse()?, val);
+                }
+            }
+
+            ConfigKind::Frozen => return Err(ConfigError::Frozen),
+        }
+
+        self.refresh()
+    }
+
     pub fn set<T>(&mut self, key: &str, value: T) -> Result<&mut Config>
     where
         T: Into<Value>,

tests/config_defaults.rs

@@ -0,0 +1,33 @@
+extern crate config;
+
+#[macro_use]
+extern crate serde_derive;
+
+use config::*;
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Settings {
+    pub db_host: String,
+}
+
+impl Default for Settings {
+    fn default() -> Self {
+        Settings {
+            db_host: String::from("default"),
+        }
+    }
+}
+
+impl Settings {
+    pub fn new() -> Result<Self, ConfigError> {
+        let mut s = Config::new();
+        s.set_defaults(Settings::default());
+        s.try_into()
+    }
+}
+
+#[test]
+fn config_with_defaults(){
+    let mut s = Settings::new().unwrap();
+    assert_eq!(s.db_host, "default");
+}