Avoid double checking of builtin's.

src/fn_call.rs

@@ -21,6 +21,7 @@ use crate::stdlib::{
     string::ToString,
     vec::Vec,
 };
+use crate::token::is_assignment_operator;
 use crate::utils::combine_hashes;
 use crate::{
     calc_native_fn_hash, calc_script_fn_hash, Dynamic, Engine, EvalAltResult, FnPtr,
@@ -285,25 +286,20 @@ impl Engine {
 
         // See if it is built in.
         if args.len() == 2 && !args[0].is_variant() && !args[1].is_variant() {
-            match run_builtin_binary_op(fn_name, args[0], args[1])? {
-                Some(v) => return Ok((v, false)),
-                None => (),
-            }
+            if is_assignment_operator(fn_name) {
+                if is_ref {
+                    // Op-assignment
+                    let (first, second) = args.split_first_mut().unwrap();
 
-            // Op-assignment?
-            if is_ref {
-                match fn_name {
-                    _ if fn_name.len() <= 1 => (),
-                    "==" | "!=" | ">=" | "<=" => (),
-                    _ if fn_name.ends_with('=') => {
-                        let (first, second) = args.split_first_mut().unwrap();
-
-                        match run_builtin_op_assignment(fn_name, first, second[0])? {
-                            Some(_) => return Ok((Dynamic::UNIT, false)),
-                            None => (),
-                        }
+                    match run_builtin_op_assignment(fn_name, first, second[0])? {
+                        Some(_) => return Ok((Dynamic::UNIT, false)),
+                        None => (),
                     }
-                    _ => (),
+                }
+            } else {
+                match run_builtin_binary_op(fn_name, args[0], args[1])? {
+                    Some(v) => return Ok((v, false)),
+                    None => (),
                 }
             }
         }

src/token.rs

@@ -1657,24 +1657,36 @@ pub fn is_valid_identifier(name: impl Iterator<Item = char>) -> bool {
     first_alphabetic
 }
 
+/// Is a text string an assignment operator?
+pub fn is_assignment_operator(op: &str) -> bool {
+    match op {
+        "+=" | "-=" | "*=" | "/=" | "<<=" | ">>=" | "&=" | "|=" | "^=" | "%=" | "**=" => true,
+        _ => false,
+    }
+}
+
+/// Is a character valid to start an identifier?
 #[cfg(feature = "unicode-xid-ident")]
 #[inline(always)]
 pub fn is_id_first_alphabetic(x: char) -> bool {
     unicode_xid::UnicodeXID::is_xid_start(x)
 }
 
+/// Is a character valid for an identifier?
 #[cfg(feature = "unicode-xid-ident")]
 #[inline(always)]
 pub fn is_id_continue(x: char) -> bool {
     unicode_xid::UnicodeXID::is_xid_continue(x)
 }
 
+/// Is a character valid to start an identifier?
 #[cfg(not(feature = "unicode-xid-ident"))]
 #[inline(always)]
 pub fn is_id_first_alphabetic(x: char) -> bool {
     x.is_ascii_alphabetic()
 }
 
+/// Is a character valid for an identifier?
 #[cfg(not(feature = "unicode-xid-ident"))]
 #[inline(always)]
 pub fn is_id_continue(x: char) -> bool {