From a7a847013e22b3b8ea370fd03a2c35bc552bb7fc Mon Sep 17 00:00:00 2001
From: Walter Bright <walter@walterbright.com>
Date: Thu, 14 Mar 2019 16:15:49 -0700
Subject: [PATCH] ChooseResult: use of unions need to be @trusted

---
 std/range/package.d | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/std/range/package.d b/std/range/package.d
index f14788f18..287f883e3 100644
--- a/std/range/package.d
+++ b/std/range/package.d
@@ -1450,9 +1450,15 @@ private struct ChooseResult(R1, R2)
             auto ref ExtraArgs extraArgs)
     {
         if (r.r1Chosen)
-            return foo(r.r1, extraArgs);
+        {
+            ref get1(return ref ChooseResult r) @trusted { return r.r1; }
+            return foo(get1(r), extraArgs);
+        }
         else
-            return foo(r.r2, extraArgs);
+        {
+            ref get2(return ref ChooseResult r) @trusted { return r.r2; }
+            return foo(get2(r), extraArgs);
+        }
     }
 
     this(bool r1Chosen, return scope R1 r1, return scope R2 r2) @trusted
@@ -1475,6 +1481,15 @@ private struct ChooseResult(R1, R2)
         }
     }
 
+    void opAssign(return scope ChooseResult r) @trusted
+    {
+        r1Chosen = r.r1Chosen;
+        if (r1Chosen)
+            r1 = r.r1;  // assigning to union members is @system
+        else
+            r2 = r.r2;
+    }
+
     // Carefully defined postblit to postblit the appropriate range
     static if (hasElaborateCopyConstructor!R1
         || hasElaborateCopyConstructor!R2)