From a5e0fe8204a8b3299507a645f3479e9ead6c6110 Mon Sep 17 00:00:00 2001
From: Ben Longbons <b.r.longbons@gmail.com>
Date: Thu, 9 Oct 2014 19:54:23 -0700
Subject: Add OPTION_IS_SOME branching macro

---
 src/compat/attr.hpp        |  6 ++++++
 src/compat/borrow.hpp      |  1 +
 src/compat/option.hpp      | 12 +++++++++++-
 src/compat/option_test.cpp | 20 ++++++++++++++++++++
 4 files changed, 38 insertions(+), 1 deletion(-)

(limited to 'src/compat')

diff --git a/src/compat/attr.hpp b/src/compat/attr.hpp
index 238a5d5..5322a14 100644
--- a/src/compat/attr.hpp
+++ b/src/compat/attr.hpp
@@ -28,4 +28,10 @@ namespace tmwa
 #else
 # define FALLTHROUGH /* fallthrough */
 #endif
+
+#define JOIN(a, b) a##b
+
+#define WITH_VAR(ty, var, expr)                                 \
+    for (bool JOIN(var, _guard) = true; JOIN(var, _guard); )    \
+        for (ty var = expr; JOIN(var, _guard); JOIN(var, _guard) = false)
 } // namespace tmwa
diff --git a/src/compat/borrow.hpp b/src/compat/borrow.hpp
index 8b23d7f..5cb6a7c 100644
--- a/src/compat/borrow.hpp
+++ b/src/compat/borrow.hpp
@@ -36,6 +36,7 @@ namespace tmwa
     {
         T *stupid;
     public:
+        Borrowed() = delete;
         explicit
         Borrowed(T *p) : stupid(p)
         {
diff --git a/src/compat/option.hpp b/src/compat/option.hpp
index 25c23eb..ad83395 100644
--- a/src/compat/option.hpp
+++ b/src/compat/option.hpp
@@ -24,6 +24,8 @@
 
 #include <utility>
 
+#include "attr.hpp"
+
 
 namespace tmwa
 {
@@ -204,6 +206,10 @@ namespace option
         {
             return repr.is_some() ? repr.ptr() : def;
         }
+        bool is_some() const
+        {
+            return repr.is_some();
+        }
 
         template<class F>
         auto move_map(F&& f) -> Option<decltype(std::forward<F>(f)(std::move(*repr.ptr())))>
@@ -365,9 +371,13 @@ namespace option
 #define TRY_UNWRAP(opt, falsy)                                  \
     ({                                                          \
         tmwa::option::RefWrapper<decltype((opt))> o = {(opt)};  \
-        if (!o.maybe_ref.ptr_or(nullptr)) falsy;                \
+        if (!o.maybe_ref.is_some()) falsy;                      \
         tmwa::option::option_unwrap(std::move(o));              \
     }).maybe_ref_fun()
+// immediately preceded by 'if'; not double-eval-safe
+#define OPTION_IS_SOME(var, expr) \
+    ((expr).is_some()) \
+    WITH_VAR(auto&, var, *(expr).ptr_or(nullptr))
 } // namespace option
 
 using option::Option;
diff --git a/src/compat/option_test.cpp b/src/compat/option_test.cpp
index e4be147..d99eda9 100644
--- a/src/compat/option_test.cpp
+++ b/src/compat/option_test.cpp
@@ -324,6 +324,26 @@ TEST(Option, unwrap)
     v = None; TRY_UNWRAP(fcl(), v = Some(1));
     v = None; TRY_UNWRAP(fr(), v = Some(1));
     v = None; TRY_UNWRAP(fcr(), v = Some(1));
+
+    v = None;
+    if OPTION_IS_SOME(o, v)
+    {
+        EXPECT_NE(o, o);
+    }
+    else
+    {
+        SUCCEED();
+    }
+
+    v = Some(1);
+    if OPTION_IS_SOME(o, v)
+    {
+        EXPECT_EQ(o, 1);
+    }
+    else
+    {
+        FAIL();
+    }
 }
 
 TEST(Option, flatten)
-- 
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