From 21c2d8bd98c85db43425ce3874dfb57783b18594 Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Fri, 9 Dec 2022 20:14:06 +0330
Subject: [PATCH] AK: Add a
 Optional::value_or_lazy_evaluated(constructor_function) API

This allows the user to avoid constructing the default value if the
optional already contains a value.
This is used by the Jakt runtime.
---
 AK/Optional.h | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/AK/Optional.h b/AK/Optional.h
index 2620498fe7..59b1dd1013 100644
--- a/AK/Optional.h
+++ b/AK/Optional.h
@@ -227,6 +227,38 @@ public:
         return move(fallback);
     }
 
+    template<typename Callback>
+    [[nodiscard]] ALWAYS_INLINE T value_or_lazy_evaluated(Callback callback) const
+    {
+        if (m_has_value)
+            return value();
+        return callback();
+    }
+
+    template<typename Callback>
+    [[nodiscard]] ALWAYS_INLINE Optional<T> value_or_lazy_evaluated_optional(Callback callback) const
+    {
+        if (m_has_value)
+            return value();
+        return callback();
+    }
+
+    template<typename Callback>
+    [[nodiscard]] ALWAYS_INLINE ErrorOr<T> try_value_or_lazy_evaluated(Callback callback) const
+    {
+        if (m_has_value)
+            return value();
+        return TRY(callback());
+    }
+
+    template<typename Callback>
+    [[nodiscard]] ALWAYS_INLINE ErrorOr<Optional<T>> try_value_or_lazy_evaluated_optional(Callback callback) const
+    {
+        if (m_has_value)
+            return value();
+        return TRY(callback());
+    }
+
     ALWAYS_INLINE T const& operator*() const { return value(); }
     ALWAYS_INLINE T& operator*() { return value(); }
 
@@ -424,6 +456,38 @@ public:
         return {};
     }
 
+    template<typename Callback>
+    [[nodiscard]] ALWAYS_INLINE T value_or_lazy_evaluated(Callback callback) const
+    {
+        if (m_pointer != nullptr)
+            return value();
+        return callback();
+    }
+
+    template<typename Callback>
+    [[nodiscard]] ALWAYS_INLINE Optional<T> value_or_lazy_evaluated_optional(Callback callback) const
+    {
+        if (m_pointer != nullptr)
+            return value();
+        return callback();
+    }
+
+    template<typename Callback>
+    [[nodiscard]] ALWAYS_INLINE ErrorOr<T> try_value_or_lazy_evaluated(Callback callback) const
+    {
+        if (m_pointer != nullptr)
+            return value();
+        return TRY(callback());
+    }
+
+    template<typename Callback>
+    [[nodiscard]] ALWAYS_INLINE ErrorOr<Optional<T>> try_value_or_lazy_evaluated_optional(Callback callback) const
+    {
+        if (m_pointer != nullptr)
+            return value();
+        return TRY(callback());
+    }
+
     template<typename F, typename MappedType = decltype(declval<F>()(declval<T&>())), auto IsErrorOr = IsSpecializationOf<MappedType, ErrorOr>, typename OptionalType = Optional<ConditionallyResultType<IsErrorOr, MappedType>>>
     ALWAYS_INLINE Conditional<IsErrorOr, ErrorOr<OptionalType>, OptionalType> map(F&& mapper)
     {