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diff --git a/indra/llcommon/always_return.h b/indra/llcommon/always_return.h
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+++ b/indra/llcommon/always_return.h
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+/**
+ * @file   always_return.h
+ * @author Nat Goodspeed
+ * @date   2023-01-20
+ * @brief  Call specified callable with arbitrary arguments, but always return
+ *         specified type.
+ * 
+ * $LicenseInfo:firstyear=2023&license=viewerlgpl$
+ * Copyright (c) 2023, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+#if ! defined(LL_ALWAYS_RETURN_H)
+#define LL_ALWAYS_RETURN_H
+
+#include <type_traits>              // std::enable_if, std::is_convertible
+
+namespace LL
+{
+
+#if __cpp_lib_is_invocable >= 201703L // C++17
+    template <typename CALLABLE, typename... ARGS>
+    using invoke_result = std::invoke_result<CALLABLE, ARGS...>;
+#else  // C++14
+    template <typename CALLABLE, typename... ARGS>
+    using invoke_result = std::result_of<CALLABLE(ARGS...)>;
+#endif // C++14
+
+    /**
+     * AlwaysReturn<T>()(some_function, some_args...) calls
+     * some_function(some_args...). It is guaranteed to return a value of type
+     * T, regardless of the return type of some_function(). If some_function()
+     * returns a type convertible to T, it will convert and return that value.
+     * Otherwise (notably if some_function() is void), AlwaysReturn returns
+     * T().
+     *
+     * When some_function() returns a type not convertible to T, if
+     * you want AlwaysReturn to return some T value other than
+     * default-constructed T(), pass that value to AlwaysReturn's constructor.
+     */
+    template <typename DESIRED>
+    class AlwaysReturn
+    {
+    public:
+        /// pass explicit default value if other than default-constructed type
+        AlwaysReturn(const DESIRED& dft=DESIRED()): mDefault(dft) {}
+
+        // callable returns a type not convertible to DESIRED, return default
+        template <typename CALLABLE, typename... ARGS,
+                  typename std::enable_if<
+                      ! std::is_convertible<
+                          typename invoke_result<CALLABLE, ARGS...>::type,
+                          DESIRED
+                      >::value,
+                      bool
+                  >::type=true>
+        DESIRED operator()(CALLABLE&& callable, ARGS&&... args)
+        {
+            // discard whatever callable(args) returns
+            std::forward<CALLABLE>(callable)(std::forward<ARGS>(args)...);
+            return mDefault;
+        }
+
+        // callable returns a type convertible to DESIRED
+        template <typename CALLABLE, typename... ARGS,
+                  typename std::enable_if<
+                      std::is_convertible<
+                          typename invoke_result<CALLABLE, ARGS...>::type,
+                          DESIRED
+                      >::value,
+                      bool
+                  >::type=true>
+        DESIRED operator()(CALLABLE&& callable, ARGS&&... args)
+        {
+            return { std::forward<CALLABLE>(callable)(std::forward<ARGS>(args)...) };
+        }
+
+    private:
+        DESIRED mDefault;
+    };
+
+    /**
+     * always_return<T>(some_function, some_args...) calls
+     * some_function(some_args...). It is guaranteed to return a value of type
+     * T, regardless of the return type of some_function(). If some_function()
+     * returns a type convertible to T, it will convert and return that value.
+     * Otherwise (notably if some_function() is void), always_return() returns
+     * T().
+     */
+    template <typename DESIRED, typename CALLABLE, typename... ARGS>
+    DESIRED always_return(CALLABLE&& callable, ARGS&&... args)
+    {
+        return AlwaysReturn<DESIRED>()(std::forward<CALLABLE>(callable),
+                                       std::forward<ARGS>(args)...);
+    }
+
+    /**
+     * make_always_return<T>(some_function) returns a callable which, when
+     * called with appropriate some_function() arguments, always returns a
+     * value of type T, regardless of the return type of some_function(). If
+     * some_function() returns a type convertible to T, the returned callable
+     * will convert and return that value. Otherwise (notably if
+     * some_function() is void), the returned callable returns T().
+     *
+     * When some_function() returns a type not convertible to T, if
+     * you want the returned callable to return some T value other than
+     * default-constructed T(), pass that value to make_always_return() as its
+     * optional second argument.
+     */
+    template <typename DESIRED, typename CALLABLE>
+    auto make_always_return(CALLABLE&& callable, const DESIRED& dft=DESIRED())
+    {
+        return
+            [dft, callable = std::forward<CALLABLE>(callable)]
+            (auto&&... args)
+            {
+                return AlwaysReturn<DESIRED>(dft)(callable,
+                                                  std::forward<decltype(args)>(args)...);
+            };
+    }
+
+} // namespace LL
+
+#endif /* ! defined(LL_ALWAYS_RETURN_H) */