Allow overloading of script functions.

README.md

@@ -365,7 +365,7 @@ fn to_int(num) {
     print("Ha! Gotcha! " + num);
 }
 
-print(to_int(123));     // what will happen?
+print(to_int(123));     // what happens?
 ```
 
 Custom types and methods
@@ -794,7 +794,7 @@ print(y.len());         // prints 0
 ```
 
 `push` and `pad` are only defined for standard built-in types.  If you want to use them with
-your own custom type, you need to define a specific override:
+your own custom type, you need to register a type-specific version:
 
 ```rust
 engine.register_fn("push",
@@ -975,9 +975,8 @@ fn add(x, y) {
 print(add(2, 3));
 ```
 
-Remember that functions defined in script always take `Dynamic` arguments (i.e. the arguments can be of any type).
-
-However, all arguments are passed by _value_, so all functions are _pure_ (i.e. they never modify their arguments).
+Functions defined in script always take `Dynamic` arguments (i.e. the arguments can be of any type).
+It is important to remember that all arguments are passed by _value_, so all functions are _pure_ (i.e. they never modify their arguments).
 Any update to an argument will **not** be reflected back to the caller. This can introduce subtle bugs, if you are not careful.
 
 ```rust
@@ -990,7 +989,7 @@ x.change();
 x == 500;       // 'x' is NOT changed!
 ```
 
-Furthermore, functions can only be defined at the top level, never inside a block or another function.
+Functions can only be defined at the top level, never inside a block or another function.
 
 ```rust
 // Top level is OK
@@ -1008,6 +1007,22 @@ fn do_addition(x) {
 }
 ```
 
+Functions can be _overloaded_ based on the number of parameters (but not parameter types, since all parameters are `Dynamic`).
+New definitions of the same name and number of parameters overwrite previous definitions.
+
+```rust
+fn abc(x,y,z) { print("Three!!! " + x + "," + y + "," + z) }
+fn abc(x) { print("One! " + x) }
+fn abc(x,y) { print("Two! " + x + "," + y) }
+fn abc() { print("None.") }
+fn abc(x) { print("HA! NEW ONE! " + x) }    // overwrites previous definition
+
+abc(1,2,3);     // prints "Three!!! 1,2,3"
+abc(42);        // prints "HA! NEW ONE! 42"
+abc(1,2);       // prints "Two!! 1,2"
+abc();          // prints "None."
+```
+
 Members and methods
 -------------------
 

src/api.rs

@@ -174,9 +174,15 @@ impl<'e> Engine<'e> {
             let statements = {
                 let AST(statements, functions) = ast;
 
-                functions.iter().for_each(|f| {
-                    engine.script_functions.push(f.clone());
-                });
+                for f in functions {
+                    match engine
+                        .script_functions
+                        .binary_search_by(|fn_def| fn_def.compare(&f.name, f.params.len()))
+                    {
+                        Ok(n) => engine.script_functions[n] = f.clone(),
+                        Err(n) => engine.script_functions.insert(n, f.clone()),
+                    }
+                }
 
                 statements
             };
@@ -253,9 +259,15 @@ impl<'e> Engine<'e> {
                 let statements = {
                     let AST(ref statements, ref functions) = ast;
 
-                    functions.iter().for_each(|f| {
-                        self.script_functions.push(f.clone());
-                    });
+                    for f in functions {
+                        match self
+                            .script_functions
+                            .binary_search_by(|fn_def| fn_def.compare(&f.name, f.params.len()))
+                        {
+                            Ok(n) => self.script_functions[n] = f.clone(),
+                            Err(n) => self.script_functions.insert(n, f.clone()),
+                        }
+                    }
 
                     statements
                 };
@@ -308,9 +320,15 @@ impl<'e> Engine<'e> {
             ast: &AST,
             args: FnCallArgs,
         ) -> Result<Dynamic, EvalAltResult> {
-            ast.1.iter().for_each(|f| {
-                engine.script_functions.push(f.clone());
-            });
+            for f in &ast.1 {
+                match engine
+                    .script_functions
+                    .binary_search_by(|fn_def| fn_def.compare(&f.name, f.params.len()))
+                {
+                    Ok(n) => engine.script_functions[n] = f.clone(),
+                    Err(n) => engine.script_functions.insert(n, f.clone()),
+                }
+            }
 
             let result = engine.call_fn_raw(name, args, None, Position::none());
 

src/engine.rs

@@ -41,7 +41,7 @@ enum IndexSourceType {
     Expression,
 }
 
-#[derive(Debug, Eq, PartialEq, Hash)]
+#[derive(Debug, Eq, PartialEq, Hash, Clone)]
 pub struct FnSpec<'a> {
     pub name: Cow<'a, str>,
     pub args: Option<Vec<TypeId>>,
@@ -82,10 +82,10 @@ impl Engine<'_> {
     pub fn new() -> Self {
         // User-friendly names for built-in types
         let type_names = [
-            (type_name::<String>(), "string"),
-            (type_name::<Dynamic>(), "dynamic"),
             #[cfg(not(feature = "no_index"))]
             (type_name::<Array>(), "array"),
+            (type_name::<String>(), "string"),
+            (type_name::<Dynamic>(), "dynamic"),
         ]
         .iter()
         .map(|(k, v)| (k.to_string(), v.to_string()))
@@ -135,22 +135,11 @@ impl Engine<'_> {
         );
 
         // First search in script-defined functions (can override built-in)
-        if let Some(func) = self
+        if let Ok(n) = self
             .script_functions
-            .iter()
-            .rev()
-            .find(|fn_def| fn_def.name == fn_name)
-            .map(|fn_def| fn_def.clone())
+            .binary_search_by(|f| f.compare(fn_name, args.len()))
         {
-            // First check number of parameters
-            if func.params.len() != args.len() {
-                return Err(EvalAltResult::ErrorFunctionArgsMismatch(
-                    fn_name.into(),
-                    func.params.len(),
-                    args.len(),
-                    pos,
-                ));
-            }
+            let func = self.script_functions[n].clone();
 
             let mut scope = Scope::new();
 
@@ -838,13 +827,9 @@ impl Engine<'_> {
             Expr::Array(contents, _) => {
                 let mut arr = Vec::new();
 
-                contents
-                    .iter()
-                    .try_for_each::<_, Result<_, EvalAltResult>>(|item| {
-                        let arg = self.eval_expr(scope, item)?;
-                        arr.push(arg);
-                        Ok(())
-                    })?;
+                for item in contents {
+                    arr.push(self.eval_expr(scope, item)?);
+                }
 
                 Ok(Box::new(arr))
             }

src/parser.rs

@@ -1944,7 +1944,15 @@ fn parse_top_level<'a>(
     while input.peek().is_some() {
         match input.peek() {
             #[cfg(not(feature = "no_function"))]
-            Some(&(Token::Fn, _)) => functions.push(parse_fn(input)?),
+            Some(&(Token::Fn, _)) => {
+                let f = parse_fn(input)?;
+
+                // Ensure list is sorted
+                match functions.binary_search_by(|fn_def| fn_def.compare(&f.name, f.params.len())) {
+                    Ok(n) => functions[n] = f,        // Override previous definition
+                    Err(n) => functions.insert(n, f), // New function definition
+                }
+            }
             _ => statements.push(parse_stmt(input)?),
         }
 

tests/internal_fn.rs

@@ -30,3 +30,25 @@ fn test_big_internal_fn() -> Result<(), EvalAltResult> {
 
     Ok(())
 }
+
+#[test]
+fn test_internal_fn_overloading() -> Result<(), EvalAltResult> {
+    let mut engine = Engine::new();
+
+    assert_eq!(
+        engine.eval::<INT>(
+            r#"
+                fn abc(x,y,z) { 2*x + 3*y + 4*z + 888 }
+                fn abc(x) { x + 42 }
+                fn abc(x,y) { x + 2*y + 88 }
+                fn abc() { 42 }
+                fn abc(x) { x - 42 }    // should override previous definition
+
+                abc() + abc(1) + abc(1,2) + abc(1,2,3)
+    "#
+        )?,
+        1002
+    );
+
+    Ok(())
+}