Use TryFrom trait instead of From trait for type conversions from JSONValue

src/lib.rs

@@ -7,7 +7,8 @@
 //!
 //! Basic usage:
 //! ```rust
-//! use naive_json_parser::{JSON, JSONArray};
+//! use std::convert::TryFrom;
+//! use naive_json_parser::{JSON, JSONArray, JSONValue};
 //!
 //! // Convert the JSON string to a `JSONValue`
 //! let result = JSON::parse("[0, 1, 2]");
@@ -17,13 +18,23 @@
 //! let result = result.unwrap();
 //!
 //! // If you want the value inside of the top `JSONValue`, you
-//! // may use the `into` or `unwrap` methods
-//! let array: JSONArray = result.clone().into(); // or
-//! let array: JSONArray = result.clone().unwrap(); // or
-//! let array = JSONArray::from(result.clone());
+//! // may use the `unwrap` method
+//! let array: JSONArray = result.clone().unwrap();
+//!
+//! // You may also try the type conversion directly, so you can handle a potential error
+//! let array = match JSONArray::try_from(result.clone()) {
+//!     Ok(a) => a,
+//!     Err(_) => todo!(),
+//! };
+//!
+//! // If you want to create a `JSONValue` from one of its wrapped types, you
+//! // may use the `from` or `into` methods
+//! let json_array = JSONValue::from(array.clone()); // or
+//! let json_array: JSONValue = array.clone().into();
 //! ```
 #![forbid(unsafe_code)]
 use std::collections::HashMap;
+use std::convert::TryFrom;
 use std::iter::FromIterator;
 use std::{char, u16};
 
@@ -79,63 +90,71 @@ impl JSONValue {
     ///
     /// # assert_eq!(str, &s);
     /// ```
-    pub fn unwrap<T: From<JSONValue>>(self) -> T {
-        T::from(self)
+    pub fn unwrap<T: TryFrom<JSONValue>>(self) -> T {
+        match T::try_from(self) {
+            Ok(val) => val,
+            Err(_) => panic!("Tried to unwrap an empty value")
+        }
     }
 }
 
-impl From<JSONValue> for JSONMap {
+impl TryFrom<JSONValue> for JSONMap {
+    type Error = &'static str;
+
     /// Extracts the `HashMap` in the `JSONValue` enum, if it exists.
-    /// Otherwise, panics.
-    fn from(val: JSONValue) -> JSONMap {
-        match val {
-            JSONValue::Object(o) => o,
-            _ => unreachable!(),
+    fn try_from(v: JSONValue) -> Result<Self, Self::Error> {
+        match v {
+            JSONValue::Object(o) => Ok(o),
+            _ => Err("Invalid type conversion")
         }
     }
 }
 
-impl From<JSONValue> for JSONArray {
+impl TryFrom<JSONValue> for JSONArray {
+    type Error = &'static str;
+
     /// Extracts the `Vec` in the `JSONValue` enum, if it exists.
-    /// Otherwise, panics.
-    fn from(val: JSONValue) -> JSONArray {
-        match val {
-            JSONValue::Array(a) => a,
-            _ => unreachable!(),
+    fn try_from(v: JSONValue) -> Result<Self, Self::Error> {
+        match v {
+            JSONValue::Array(a) => Ok(a),
+            _ => Err("Invalid type conversion")
         }
     }
 }
 
-impl From<JSONValue> for f64 {
+impl TryFrom<JSONValue> for f64 {
+    type Error = &'static str;
+
     /// Extracts the `f64` in the `JSONValue` enum, if it exists.
-    /// Otherwise, panics.
-    fn from(val: JSONValue) -> f64 {
-        match val {
-            JSONValue::Number(n) => n,
-            _ => unreachable!(),
+    fn try_from(v: JSONValue) -> Result<Self, Self::Error> {
+        match v {
+            JSONValue::Number(n) => Ok(n),
+            _ => Err("Invalid type conversion")
         }
     }
 }
 
-impl From<JSONValue> for String {
+impl TryFrom<JSONValue> for String {
+    type Error = &'static str;
+
     /// Extracts the `String` in the `JSONValue` enum, if it exists.
-    /// Otherwise, panics.
-    fn from(val: JSONValue) -> String {
-        match val {
-            JSONValue::String(s) => s,
-            _ => unreachable!(),
+    fn try_from(v: JSONValue) -> Result<Self, Self::Error> {
+        match v {
+            JSONValue::String(s) => Ok(s),
+            _ => Err("Invalid type conversion")
         }
     }
 }
 
-impl From<JSONValue> for bool {
-    /// Extracts the `bool` value from the `JSONValue` enum, if it exists.
-    /// Otherwise, panics.
-    fn from(val: JSONValue) -> bool {
-        match val {
-            JSONValue::True => true,
-            JSONValue::False => false,
-            _ => unreachable!(),
+impl TryFrom<JSONValue> for bool {
+    type Error = &'static str;
+
+    /// Extracts the `bool` in the `JSONValue` enum, if it exists.
+    fn try_from(v: JSONValue) -> Result<Self, Self::Error> {
+        match v {
+            JSONValue::True => Ok(true),
+            JSONValue::False => Ok(false),
+            _ => Err("Invalid type conversion")
         }
     }
 }
@@ -320,7 +339,7 @@ impl JSON {
             self.skip_whitespace();
             self.eat(':')?;
 
-            let key = maybe_key.unwrap().into();
+            let key = maybe_key.unwrap().unwrap();
             let value = self.parse_value()?;
 
             result.insert(key, value);

tests/happy_paths.rs

@@ -1,10 +1,11 @@
 use naive_json_parser::JSONValue::{Array, False, Null, Number, Object, True};
 use naive_json_parser::*;
 use std::collections::HashMap;
+use std::convert::TryFrom;
 use std::f64::consts::PI;
 
 #[test]
-fn value_conversion() {
+fn value_conversion() -> Result<(), &'static str> {
     let map: JSONMap = HashMap::new();
     let num = 9.380831539;
     let str = "applesauce";
@@ -14,13 +15,15 @@ fn value_conversion() {
         JSONValue::from(str),
     ];
 
-    assert_eq!(map.clone(), JSONMap::from(JSONValue::from(map.clone())));
-    assert_eq!(num, f64::from(JSONValue::from(num)));
-    assert_eq!(String::from(str), String::from(JSONValue::from(str)));
-    assert_eq!(arr.clone(), JSONArray::from(JSONValue::from(arr.clone())));
-    assert_eq!(true, bool::from(JSONValue::from(true)));
-    assert_eq!(false, bool::from(JSONValue::from(false)));
+    assert_eq!(map.clone(), JSONMap::try_from(JSONValue::from(map.clone()))?);
+    assert_eq!(num, f64::try_from(JSONValue::from(num))?);
+    assert_eq!(String::from(str), String::try_from(JSONValue::from(str))?);
+    assert_eq!(arr.clone(), JSONArray::try_from(JSONValue::from(arr.clone()))?);
+    assert_eq!(true, bool::try_from(JSONValue::from(true))?);
+    assert_eq!(false, bool::try_from(JSONValue::from(false))?);
     assert_eq!((), <()>::from(JSONValue::from(())));
+
+    Ok(())
 }
 
 #[test]