Allow binding of this pointer in FnPtr calls.

RELEASES.md

@@ -9,6 +9,7 @@ New features
 
 * `call` can now be called function-call style for function pointers - this is to handle builds with `no_object`.
 * Disallow many keywords as variables, such as `print`, `eval`, `call`, `this` etc.
+* `x.call(f, ...)` allows binding `x` to `this` for the function referenced by the function pointer `f`.
 
 
 Version 0.17.0

doc/src/language/fn-ptr.md

@@ -66,20 +66,18 @@ Because of their dynamic nature, function pointers cannot refer to functions in
 See [function namespaces] for more details.
 
 ```rust
-import "foo" as f;          // assume there is 'f::do_something()'
+import "foo" as f;          // assume there is 'f::do_work()'
 
-f::do_something();          // works!
+f::do_work();               // works!
 
-let p = Fn("f::do_something");
+let p = Fn("f::do_work");   // error: invalid function name
 
-p.call();                   // error: function not found - 'f::do_something'
+fn do_work_now() {          // call it from a local function
-
-fn do_something_now() {     // call it from a local function
     import "foo" as f;
-    f::do_something();
+    f::do_work();
 }
 
-let p = Fn("do_something_now");
+let p = Fn("do_work_now");
 
 p.call();                   // works!
 ```
@@ -134,3 +132,35 @@ let func = sign(x) + 1;
 // Dynamic dispatch
 map[func].call(42);
 ```
+
+
+Binding the `this` Pointer
+-------------------------
+
+When `call` is called as a _method_ but not on a `FnPtr` value, it is possible to dynamically dispatch
+to a function call while binding the object in the method call to the `this` pointer of the function.
+
+To achieve this, pass the `FnPtr` value as the _first_ argument to `call`:
+
+```rust
+fn add(x) { this += x; }    // define function which uses 'this'
+
+let func = Fn("add");       // function pointer to 'add'
+
+func.call(1);               // error: 'this' pointer is not bound
+
+let x = 41;
+
+func.call(x, 1);            // error: function 'add (i64, i64)' not found
+
+call(func, x, 1);           // error: function 'add (i64, i64)' not found
+
+x.call(func, 1);            // 'this' is bound to 'x', dispatched to 'func'
+
+x == 42;
+```
+
+Beware that this only works for _method-call_ style.  Normal function-call style cannot bind
+the `this` pointer (for syntactic reasons).
+
+Therefore, obviously, binding the `this` pointer is unsupported under [`no_function`].

src/engine.rs

@@ -96,7 +96,7 @@ pub const MARKER_BLOCK: &str = "$block$";
 pub const MARKER_IDENT: &str = "$ident$";
 
 #[cfg(feature = "internals")]
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Hash)]
 pub struct Expression<'a>(&'a Expr);
 
 #[cfg(feature = "internals")]
@@ -1088,10 +1088,10 @@ impl Engine {
         let idx = idx_val.downcast_mut::<StaticVec<Dynamic>>().unwrap();
         let mut fn_name = name.as_ref();
 
-        // Check if it is a FnPtr call
         let (result, updated) = if fn_name == KEYWORD_FN_PTR_CALL && obj.is::<FnPtr>() {
+            // FnPtr call
             // Redirect function name
-            fn_name = obj.as_str().unwrap();
+            let fn_name = obj.as_str().unwrap();
             // Recalculate hash
             let hash = calc_fn_hash(empty(), fn_name, idx.len(), empty());
             // Arguments are passed as-is
@@ -1102,6 +1102,26 @@ impl Engine {
             self.exec_fn_call(
                 state, lib, fn_name, *native, hash, args, false, false, def_val, level,
             )
+        } else if fn_name == KEYWORD_FN_PTR_CALL && idx.len() > 0 && idx[0].is::<FnPtr>() {
+            // FnPtr call on object
+            // Redirect function name
+            let fn_name = idx[0]
+                .downcast_ref::<FnPtr>()
+                .unwrap()
+                .get_fn_name()
+                .clone();
+            // Recalculate hash
+            let hash = calc_fn_hash(empty(), &fn_name, idx.len() - 1, empty());
+            // Replace the first argument with the object pointer
+            let mut arg_values = once(obj)
+                .chain(idx.iter_mut().skip(1))
+                .collect::<StaticVec<_>>();
+            let args = arg_values.as_mut();
+
+            // Map it to name(args) in function-call style
+            self.exec_fn_call(
+                state, lib, &fn_name, *native, hash, args, is_ref, true, def_val, level,
+            )
         } else {
             let redirected: Option<ImmutableString>;
             let mut hash = *hash;

src/error.rs

@@ -98,6 +98,8 @@ pub enum ParseErrorType {
     PropertyExpected,
     /// Missing a variable name after the `let`, `const` or `for` keywords.
     VariableExpected,
+    /// An identifier is a reserved keyword.
+    Reserved(String),
     /// Missing an expression. Wrapped value is the expression type.
     ExprExpected(String),
     /// Defining a function `fn` in an appropriate place (e.g. inside another function).
@@ -163,6 +165,7 @@ impl ParseErrorType {
             Self::ForbiddenConstantExpr(_) => "Expecting a constant",
             Self::PropertyExpected => "Expecting name of a property",
             Self::VariableExpected => "Expecting name of a variable",
+            Self::Reserved(_) => "Invalid use of reserved keyword",
             Self::ExprExpected(_) => "Expecting an expression",
             Self::FnMissingName => "Expecting name in function declaration",
             Self::FnMissingParams(_) => "Expecting parameters in function declaration",
@@ -224,6 +227,7 @@ impl fmt::Display for ParseErrorType {
             Self::LiteralTooLarge(typ, max) => {
                 write!(f, "{} exceeds the maximum limit ({})", typ, max)
             }
+            Self::Reserved(s) => write!(f, "'{}' is a reserved keyword", s),
             _ => f.write_str(self.desc()),
         }
     }

src/parser.rs

@@ -25,6 +25,7 @@ use crate::stdlib::{
     char,
     collections::HashMap,
     fmt, format,
+    hash::Hash,
     iter::empty,
     mem,
     num::NonZeroUsize,
@@ -340,7 +341,7 @@ impl fmt::Display for FnAccess {
 }
 
 /// A scripted function definition.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Hash)]
 pub struct ScriptFnDef {
     /// Function name.
     pub name: String,
@@ -374,7 +375,7 @@ impl fmt::Display for ScriptFnDef {
 }
 
 /// `return`/`throw` statement.
-#[derive(Debug, Eq, PartialEq, Hash, Clone, Copy)]
+#[derive(Debug, Eq, PartialEq, Clone, Copy, Hash)]
 pub enum ReturnType {
     /// `return` statement.
     Return,
@@ -478,7 +479,7 @@ impl ParseSettings {
 ///
 /// Each variant is at most one pointer in size (for speed),
 /// with everything being allocated together in one single tuple.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Hash)]
 pub enum Stmt {
     /// No-op.
     Noop(Position),
@@ -590,6 +591,13 @@ impl fmt::Debug for CustomExpr {
     }
 }
 
+#[cfg(feature = "internals")]
+impl Hash for CustomExpr {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        self.0.hash(state);
+    }
+}
+
 /// An expression.
 ///
 /// Each variant is at most one pointer in size (for speed),
@@ -665,6 +673,18 @@ impl Default for Expr {
     }
 }
 
+impl Hash for Expr {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        match self {
+            Self::FloatConstant(x) => {
+                state.write(&x.0.to_le_bytes());
+                x.1.hash(state);
+            }
+            _ => self.hash(state),
+        }
+    }
+}
+
 impl Expr {
     /// Get the `Dynamic` value of a constant expression.
     ///
@@ -1345,24 +1365,27 @@ fn parse_map_literal(
                 eat_token(input, Token::RightBrace);
                 break;
             }
-            _ => {
+            _ => (),
+        }
+
         let (name, pos) = match input.next().unwrap() {
             (Token::Identifier(s), pos) => (s, pos),
             (Token::StringConstant(s), pos) => (s, pos),
+            (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
+                return Err(PERR::Reserved(s).into_err(pos));
+            }
             (Token::LexError(err), pos) => return Err(err.into_err(pos)),
             (_, pos) if map.is_empty() => {
-                        return Err(PERR::MissingToken(
+                return Err(
-                            Token::RightBrace.into(),
+                    PERR::MissingToken(Token::RightBrace.into(), MISSING_RBRACE.into())
-                            MISSING_RBRACE.into(),
+                        .into_err(pos),
-                        )
+                );
-                        .into_err(pos))
             }
             (Token::EOF, pos) => {
-                        return Err(PERR::MissingToken(
+                return Err(
-                            Token::RightBrace.into(),
+                    PERR::MissingToken(Token::RightBrace.into(), MISSING_RBRACE.into())
-                            MISSING_RBRACE.into(),
+                        .into_err(pos),
-                        )
+                );
-                        .into_err(pos))
             }
             (_, pos) => return Err(PERR::PropertyExpected.into_err(pos)),
         };
@@ -1392,8 +1415,6 @@ fn parse_map_literal(
 
         let expr = parse_expr(input, state, lib, settings.level_up())?;
         map.push(((Into::<ImmutableString>::into(name), pos), expr));
-            }
-        }
 
         match input.peek().unwrap() {
             (Token::Comma, _) => {
@@ -1477,6 +1498,9 @@ fn parse_primary(
                 Expr::Variable(Box::new(((s, settings.pos), None, 0, None)))
             }
         }
+        Token::Reserved(s) if is_valid_identifier(s.chars()) => {
+            return Err(PERR::Reserved(s).into_err(settings.pos));
+        }
         Token::LeftParen => parse_paren_expr(input, state, lib, settings.level_up())?,
         #[cfg(not(feature = "no_index"))]
         Token::LeftBracket => parse_array_literal(input, state, lib, settings.level_up())?,
@@ -1488,7 +1512,7 @@ fn parse_primary(
         _ => {
             return Err(
                 PERR::BadInput(format!("Unexpected '{}'", token.syntax())).into_err(settings.pos)
-            )
+            );
         }
     };
 
@@ -1526,6 +1550,9 @@ fn parse_primary(
 
                     Expr::Variable(Box::new(((id2, pos2), modules, 0, index)))
                 }
+                (Token::Reserved(id2), pos2) if is_valid_identifier(id2.chars()) => {
+                    return Err(PERR::Reserved(id2).into_err(pos2));
+                }
                 (_, pos2) => return Err(PERR::VariableExpected.into_err(pos2)),
             },
             // Indexing
@@ -2112,6 +2139,9 @@ fn parse_expr(
                             (Token::Identifier(s), pos) => {
                                 exprs.push(Expr::Variable(Box::new(((s, pos), None, 0, None))));
                             }
+                            (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
+                                return Err(PERR::Reserved(s).into_err(pos));
+                            }
                             (_, pos) => return Err(PERR::VariableExpected.into_err(pos)),
                         },
                         MARKER_EXPR => exprs.push(parse_expr(input, state, lib, settings)?),
@@ -2279,10 +2309,12 @@ fn parse_for(
     let name = match input.next().unwrap() {
         // Variable name
         (Token::Identifier(s), _) => s,
+        // Reserved keyword
+        (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
+            return Err(PERR::Reserved(s).into_err(pos));
+        }
         // Bad identifier
         (Token::LexError(err), pos) => return Err(err.into_err(pos)),
-        // EOF
-        (Token::EOF, pos) => return Err(PERR::VariableExpected.into_err(pos)),
         // Not a variable name
         (_, pos) => return Err(PERR::VariableExpected.into_err(pos)),
     };
@@ -2329,6 +2361,9 @@ fn parse_let(
     // let name ...
     let (name, pos) = match input.next().unwrap() {
         (Token::Identifier(s), pos) => (s, pos),
+        (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
+            return Err(PERR::Reserved(s).into_err(pos));
+        }
         (Token::LexError(err), pos) => return Err(err.into_err(pos)),
         (_, pos) => return Err(PERR::VariableExpected.into_err(pos)),
     };
@@ -2398,6 +2433,9 @@ fn parse_import(
     // import expr as name ...
     let (name, _) = match input.next().unwrap() {
         (Token::Identifier(s), pos) => (s, pos),
+        (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
+            return Err(PERR::Reserved(s).into_err(pos));
+        }
         (Token::LexError(err), pos) => return Err(err.into_err(pos)),
         (_, pos) => return Err(PERR::VariableExpected.into_err(pos)),
     };
@@ -2422,6 +2460,9 @@ fn parse_export(
     loop {
         let (id, id_pos) = match input.next().unwrap() {
             (Token::Identifier(s), pos) => (s.clone(), pos),
+            (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
+                return Err(PERR::Reserved(s).into_err(pos));
+            }
             (Token::LexError(err), pos) => return Err(err.into_err(pos)),
             (_, pos) => return Err(PERR::VariableExpected.into_err(pos)),
         };
@@ -2429,6 +2470,10 @@ fn parse_export(
         let rename = if match_token(input, Token::As)? {
             match input.next().unwrap() {
                 (Token::Identifier(s), pos) => Some((s.clone(), pos)),
+                (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
+                    return Err(PERR::Reserved(s).into_err(pos));
+                }
+                (Token::LexError(err), pos) => return Err(err.into_err(pos)),
                 (_, pos) => return Err(PERR::VariableExpected.into_err(pos)),
             }
         } else {

src/token.rs

@@ -279,8 +279,6 @@ impl Token {
                 Or => "||",
                 Ampersand => "&",
                 And => "&&",
-                #[cfg(not(feature = "no_function"))]
-                Fn => "fn",
                 Continue => "continue",
                 Break => "break",
                 Return => "return",
@@ -301,8 +299,12 @@ impl Token {
                 ModuloAssign => "%=",
                 PowerOf => "~",
                 PowerOfAssign => "~=",
+
+                #[cfg(not(feature = "no_function"))]
+                Fn => "fn",
                 #[cfg(not(feature = "no_function"))]
                 Private => "private",
+
                 #[cfg(not(feature = "no_module"))]
                 Import => "import",
                 #[cfg(not(feature = "no_module"))]
@@ -359,8 +361,6 @@ impl Token {
             "||" => Or,
             "&" => Ampersand,
             "&&" => And,
-            #[cfg(not(feature = "no_function"))]
-            "fn" => Fn,
             "continue" => Continue,
             "break" => Break,
             "return" => Return,
@@ -381,14 +381,25 @@ impl Token {
             "%=" => ModuloAssign,
             "~" => PowerOf,
             "~=" => PowerOfAssign,
+
+            #[cfg(not(feature = "no_function"))]
+            "fn" => Fn,
             #[cfg(not(feature = "no_function"))]
             "private" => Private,
+
             #[cfg(not(feature = "no_module"))]
             "import" => Import,
             #[cfg(not(feature = "no_module"))]
             "export" => Export,
             #[cfg(not(feature = "no_module"))]
             "as" => As,
+
+            #[cfg(feature = "no_function")]
+            "fn" | "private" => Reserved(syntax.into()),
+
+            #[cfg(feature = "no_module")]
+            "import" | "export" | "as" => Reserved(syntax.into()),
+
             "===" | "!==" | "->" | "<-" | "=>" | ":=" | "::<" | "(*" | "*)" | "#" => {
                 Reserved(syntax.into())
             }

src/utils.rs

@@ -156,6 +156,12 @@ impl<T> Drop for StaticVec<T> {
     }
 }
 
+impl<T: Hash> Hash for StaticVec<T> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.iter().for_each(|x| x.hash(state));
+    }
+}
+
 impl<T> Default for StaticVec<T> {
     fn default() -> Self {
         Self {

tests/call_fn.rs

@@ -116,7 +116,7 @@ fn test_anonymous_fn() -> Result<(), Box<EvalAltResult>> {
 
 #[test]
 #[cfg(not(feature = "no_object"))]
-fn test_fn_ptr() -> Result<(), Box<EvalAltResult>> {
+fn test_fn_ptr_raw() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
 
     engine.register_raw_fn(

tests/fn_ptr.rs

@@ -0,0 +1,80 @@
+use rhai::{Engine, EvalAltResult, RegisterFn, INT};
+
+#[test]
+fn test_fn_ptr() -> Result<(), Box<EvalAltResult>> {
+    let mut engine = Engine::new();
+
+    engine.register_fn("bar", |x: &mut INT, y: INT| *x += y);
+
+    #[cfg(not(feature = "no_object"))]
+    assert_eq!(
+        engine.eval::<INT>(
+            r#"
+                let f = Fn("bar");
+                let x = 40;
+                f.call(x, 2);
+                x
+            "#
+        )?,
+        40
+    );
+
+    #[cfg(not(feature = "no_object"))]
+    assert_eq!(
+        engine.eval::<INT>(
+            r#"
+                let f = Fn("bar");
+                let x = 40;
+                x.call(f, 2);
+                x
+            "#
+        )?,
+        42
+    );
+
+    assert_eq!(
+        engine.eval::<INT>(
+            r#"
+                let f = Fn("bar");
+                let x = 40;
+                call(f, x, 2);
+                x
+            "#
+        )?,
+        42
+    );
+
+    #[cfg(not(feature = "no_function"))]
+    #[cfg(not(feature = "no_object"))]
+    assert_eq!(
+        engine.eval::<INT>(
+            r#"
+                fn foo(x) { this += x; }
+
+                let f = Fn("foo");
+                let x = 40;
+                x.call(f, 2);
+                x
+            "#
+        )?,
+        42
+    );
+
+    #[cfg(not(feature = "no_function"))]
+    assert!(matches!(
+        *engine
+            .eval::<INT>(
+                r#"
+                fn foo(x) { this += x; }
+
+                let f = Fn("foo");
+                call(f, 2);
+                x
+            "#
+            )
+            .expect_err("should error"),
+        EvalAltResult::ErrorInFunctionCall(fn_name, err, _) if fn_name == "foo" && matches!(*err, EvalAltResult::ErrorUnboundedThis(_))
+    ));
+
+    Ok(())
+}