From 442e5423479608e417011a1cd34e9a304eda8153 Mon Sep 17 00:00:00 2001
From: Guillaume Pinot <guillaume.pinot@citodi.fr>
Date: Wed, 15 Sep 2021 17:37:20 +0200
Subject: [PATCH] Convert an iterator of Into<LinearExpr> to a LinearExpr

---
 Cargo.toml     |  2 +-
 src/builder.rs | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/Cargo.toml b/Cargo.toml
index a769ec6..368bda5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "cp_sat"
-version = "0.3.1"
+version = "0.3.2"
 edition = "2018"
 description = "Rust bindings to the Google CP-SAT constraint programming solver."
 documentation = "https://docs.rs/cp_sat"
diff --git a/src/builder.rs b/src/builder.rs
index 7b63ee7..5cc2c1e 100644
--- a/src/builder.rs
+++ b/src/builder.rs
@@ -877,6 +877,11 @@ pub struct Constraint(usize);
 ///         _ => expr -= LinearExpr::from([(42, v), (1337, y1)]) + 5,
 ///     }
 /// }
+///
+/// // an iterator of `Into<LinearExpr>` can be collected or extended,
+/// // meaning summing the elements
+/// model.maximize(vars.iter().copied().collect::<LinearExpr>()); // means sum(vars)
+/// expr.extend(vars.iter().map(|&v| (2, v))); // means expr += sum_vars(2 * v)
 /// ```
 #[derive(Clone, Default, Debug)]
 pub struct LinearExpr {
@@ -974,3 +979,18 @@ impl From<LinearExpr> for proto::LinearExpressionProto {
         }
     }
 }
+
+impl<T: Into<LinearExpr>> std::iter::Extend<T> for LinearExpr {
+    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+        for e in iter {
+            *self += e;
+        }
+    }
+}
+impl<T: Into<LinearExpr>> std::iter::FromIterator<T> for LinearExpr {
+    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
+        let mut res = LinearExpr::default();
+        res.extend(iter);
+        res
+    }
+}