From 9c6cea3c9f827e1dc32340f1144c24569fa98ffd Mon Sep 17 00:00:00 2001
From: Stephen Chung <schungx@live.com>
Date: Sat, 14 Aug 2021 14:56:15 +0800
Subject: [PATCH] Add Scope::set_or_push.

---
 CHANGELOG.md |  1 +
 src/scope.rs | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index dbfdbdb6..93f20647 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@ Enhancements
 * `ln` for `Decimal` is now checked and won't panic.
 * `Scope::set_value` now takes anything that implements `Into<Cow<str>>`.
 * Added `Scope::is_constant` to check if a variable is constant.
+* Added `Scope::set_or_push` to add a new variable only if one doesn't already exist.
 
 
 Version 1.0.2
diff --git a/src/scope.rs b/src/scope.rs
index 33bf4600..cb13ccab 100644
--- a/src/scope.rs
+++ b/src/scope.rs
@@ -363,6 +363,51 @@ impl<'a> Scope<'a> {
             AccessMode::ReadOnly => Some(true),
         })
     }
+    /// Update the value of the named entry in the [`Scope`] if it already exists and is not constant.
+    /// Push a new entry with the value into the [`Scope`] if the name doesn't exist or if the
+    /// existing entry is constant.
+    ///
+    /// Search starts backwards from the last, and only the first entry matching the specified name is updated.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use rhai::Scope;
+    ///
+    /// let mut my_scope = Scope::new();
+    ///
+    /// my_scope.set_or_push("x", 42_i64);
+    /// assert_eq!(my_scope.get_value::<i64>("x").unwrap(), 42);
+    /// assert_eq!(my_scope.len(), 1);
+    ///
+    /// my_scope.set_or_push("x", 0_i64);
+    /// assert_eq!(my_scope.get_value::<i64>("x").unwrap(), 0);
+    /// assert_eq!(my_scope.len(), 1);
+    ///
+    /// my_scope.set_or_push("y", 123_i64);
+    /// assert_eq!(my_scope.get_value::<i64>("y").unwrap(), 123);
+    /// assert_eq!(my_scope.len(), 2);
+    /// ```
+    #[inline]
+    pub fn set_or_push(
+        &mut self,
+        name: impl AsRef<str> + Into<Cow<'a, str>>,
+        value: impl Variant + Clone,
+    ) -> &mut Self {
+        match self.get_index(name.as_ref()) {
+            None | Some((_, AccessMode::ReadOnly)) => {
+                self.push(name, value);
+            }
+            Some((index, AccessMode::ReadWrite)) => {
+                let value_ref = self
+                    .values
+                    .get_mut(index)
+                    .expect("never fails because the index is returned by `get_index`");
+                *value_ref = Dynamic::from(value);
+            }
+        }
+        self
+    }
     /// Update the value of the named entry in the [`Scope`].
     ///
     /// Search starts backwards from the last, and only the first entry matching the specified name is updated.