From 7e8e2ef0be2eebc7f872ea37620dc1b60d62197f Mon Sep 17 00:00:00 2001
From: Steven Le Rouzic <steven.lerouzic@gmail.com>
Date: Sat, 2 Nov 2024 20:08:07 +0100
Subject: Add option::and_then

---
 asl/option.hpp | 37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

(limited to 'asl/option.hpp')

diff --git a/asl/option.hpp b/asl/option.hpp
index ab88992..ebb9eef 100644
--- a/asl/option.hpp
+++ b/asl/option.hpp
@@ -3,6 +3,7 @@
 #include "asl/assert.hpp"
 #include "asl/meta.hpp"
 #include "asl/maybe_uninit.hpp"
+#include "asl/functional.hpp"
 
 namespace asl
 {
@@ -334,7 +335,6 @@ public:
 
     constexpr bool has_value() const { return m_has_value; }
 
-    // @Todo Do we want this on rvalues? Or maybe some kind of unwrap?
     constexpr T&& value() &&
     {
         ASL_ASSERT(m_has_value); // @Todo Release assert
@@ -389,13 +389,46 @@ public:
     }
 
     template<typename... Args>
-    T& emplace(Args&&... args) &
+    constexpr T& emplace(Args&&... args) &
         requires constructible<T, Args&&...>
     {
         if (m_has_value) { reset(); }
         construct(ASL_FWD(args)...);
         return value();
     }
+
+    template<typename F>
+    constexpr auto and_then(F&& f) &
+        requires is_option<result_of_t<F(T&)>>
+    {
+        if (has_value())
+        {
+            return invoke(ASL_FWD(f), value());
+        }
+        return un_cvref_t<result_of_t<F(T&)>>{};
+    }
+
+    template<typename F>
+    constexpr auto and_then(F&& f) const&
+        requires is_option<result_of_t<F(const T&)>>
+    {
+        if (has_value())
+        {
+            return invoke(ASL_FWD(f), value());
+        }
+        return un_cvref_t<result_of_t<F(const T&)>>{};
+    }
+
+    template<typename F>
+    constexpr auto and_then(F&& f) &&
+        requires is_option<result_of_t<F(T)>>
+    {
+        if (has_value())
+        {
+            return invoke(ASL_FWD(f), ASL_MOVE(value()));
+        }
+        return un_cvref_t<result_of_t<F(T)>>{};
+    }
 };
 
 template<typename T>
-- 
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