Add get_parameter method.

r2r/src/error.rs

@@ -127,6 +127,18 @@ pub enum Error {
 
     #[error("Parameter {name} conversion failed: {msg}")]
     ParameterValueConv { name: String, msg: String },
+
+    #[error("Expected parameter {name} is not set")]
+    ParameterNotSet { name: String },
+
+    #[error(
+        "Parameter {name} was expected to be of type {expected_type} but was of type {actual_type}"
+    )]
+    ParameterWrongType {
+        name: String,
+        expected_type: &'static str,
+        actual_type: &'static str,
+    },
 }
 
 impl Error {

r2r/src/nodes.rs

@@ -541,6 +541,30 @@ impl Node {
         future::ready(())
     }
 
+    /// Fetch a single ROS parameter.
+    pub fn get_parameter<T>(&self, name: &str) -> Result<T>
+    where
+        ParameterValue: TryInto<T, Error = WrongParameterType>,
+    {
+        let params = self.params.lock().unwrap();
+        let parameter = params.get(name).ok_or(Error::ParameterNotSet {
+            name: name.to_string(),
+        })?;
+
+        let value: T =
+            parameter
+                .value
+                .clone()
+                .try_into()
+                .map_err(|error: WrongParameterType| Error::ParameterWrongType {
+                    name: name.to_string(),
+                    expected_type: error.expected_type_name,
+                    actual_type: error.actual_type_name,
+                })?;
+
+        Ok(value)
+    }
+
     /// Subscribe to a ROS topic.
     ///
     /// This function returns a `Stream` of ros messages.

r2r/src/parameters.rs

@@ -22,8 +22,8 @@ pub enum ParameterValue {
 
 #[derive(Debug)]
 pub struct WrongParameterType {
-    expected_type_name: &'static str,
-    actual_type_name: &'static str,
+    pub expected_type_name: &'static str,
+    pub actual_type_name: &'static str,
 }
 
 impl std::error::Error for WrongParameterType {}