From 4900f7a7533ca0d70db7dd5cb40d3fc8c5996a04 Mon Sep 17 00:00:00 2001
From: Determinant <ted.sybil@gmail.com>
Date: Wed, 31 Jan 2018 17:45:09 -0500
Subject: update to a better interface and reduce the use of type erasures

---
 promise.hpp | 231 ++++++++++++++++++++++++++++++++++++------------------------
 test.cpp    |  38 +++++-----
 2 files changed, 158 insertions(+), 111 deletions(-)

diff --git a/promise.hpp b/promise.hpp
index 397ef70..b9f5cfc 100644
--- a/promise.hpp
+++ b/promise.hpp
@@ -6,6 +6,17 @@
 #include <any>
 #include <functional>
 
+template <typename T>
+struct function_traits:
+    public function_traits<decltype(&T::operator())> {};
+
+template <typename ClassType, typename ReturnType, typename ArgType>
+struct function_traits<ReturnType(ClassType::*)(ArgType) const>
+{
+    using ret_type = ReturnType;
+    using arg_type = ArgType;
+};
+
 /** Implement type-safe Promise primitives similar to the ones specified by
  * Javascript A+. */
 namespace promise {
@@ -20,7 +31,9 @@ namespace promise {
     class promise_t {
         std::shared_ptr<Promise> ptr;
         public:
-        promise_t(function<void(promise_t)> callback) {
+
+        template<typename Func>
+        promise_t(Func callback) {
             ptr = std::make_shared<Promise>();
             callback(*this);
         }
@@ -28,24 +41,25 @@ namespace promise {
         template<typename T> inline void resolve(T result) const;
         template<typename T> inline void reject(T reason) const;
 
-        template<typename F_, typename F = pm_any_t, typename R_, typename R = pm_any_t>
-        inline promise_t then(function<F_(pm_any_t)> fulfilled_callback,
-                        function<R_(pm_any_t)> rejected_callback) const;
+        template<typename FuncFulfilled, typename FuncRejected>
+        inline promise_t then_any(FuncFulfilled fulfilled_callback,
+                                FuncRejected rejected_callback) const;
 
-        template<typename F_, typename F = pm_any_t>
-        inline promise_t then(function<F_(pm_any_t)> fulfilled_callback) const;
+        template<typename FuncFulfilled>
+        inline promise_t then_any(FuncFulfilled fulfilled_callback) const;
 
-        template<typename R_, typename R = pm_any_t>
-        inline promise_t fail(function<R_(pm_any_t)> rejected_callback) const;
+        template<typename FuncRejected>
+        inline promise_t fail_any(FuncRejected rejected_callback) const;
 
-        template<typename F_, typename F>
-        inline promise_t then(function<F_(F)> on_fulfilled) const;
+        template<typename FuncFulfilled>
+        inline promise_t then(FuncFulfilled on_fulfilled) const;
 
-        template<typename F_, typename F, typename R_, typename R>
-        inline promise_t then(function<F_(F)> on_fulfilled, function<R_(R)> on_rejected) const;
+        template<typename FuncFulfilled, typename FuncRejected>
+        inline promise_t then(FuncFulfilled on_fulfilled,
+                            FuncRejected on_rejected) const;
 
-        template<typename F_, typename F>
-        inline promise_t fail(function<F_(F)> on_fulfilled) const;
+        template<typename FuncRejected>
+        inline promise_t fail(FuncRejected on_rejected) const;
     };
 
 #define PROMISE_ERR_INVALID_STATE do {throw std::runtime_error("invalid promise state");} while (0)
@@ -93,50 +107,58 @@ namespace promise {
             rejected_callbacks.push_back(cb);
         }
 
-        function<void()> gen_on_fulfilled(
-                function<promise_t(pm_any_t)> on_fulfilled,
-                const promise_t &npm) {
-            return [this, on_fulfilled, npm]() {
-                on_fulfilled(result).then(
-                    function<None(pm_any_t)>([npm] (pm_any_t result_) {
+        template<typename Func>
+        typename std::enable_if<
+            std::is_same<typename function_traits<Func>::ret_type,
+                         promise_t>::value>::type
+        gen_on_fulfilled(Func on_fulfilled, const promise_t &npm, function<void()> &ret) {
+            ret = [this, on_fulfilled, npm]() {
+                on_fulfilled(result).then_any(
+                    [npm] (pm_any_t result_) {
                         npm.resolve(result_);
-                        return none;
-                    }),
-                    function<None(pm_any_t)>([npm] (pm_any_t reason_) {
+                        return pm_any_t(none);
+                    },
+                    [npm] (pm_any_t reason_) {
                         npm.reject(reason_);
-                        return none;
-                    }));
+                        return pm_any_t(none);
+                    });
             };
         }
 
-        function<void()> gen_on_fulfilled(
-                function<pm_any_t(pm_any_t)> on_fulfilled,
-                const promise_t &npm) {
-            return [this, on_fulfilled, npm]() {
+        template<typename Func>
+        typename std::enable_if<
+            std::is_same<typename function_traits<Func>::ret_type,
+                         pm_any_t>::value>::type
+        gen_on_fulfilled(Func on_fulfilled, const promise_t &npm, function<void()> &ret) {
+            ret = [this, on_fulfilled, npm]() {
                 npm.resolve(on_fulfilled(result));
             };
         }
 
-        function<void()> gen_on_rejected(
-                function<promise_t(pm_any_t)> on_rejected,
-                const promise_t &npm) {
-            return [this, on_rejected, npm]() {
-                on_rejected(reason).then(
-                    function<None(pm_any_t)>([npm] (pm_any_t result_) {
+        template<typename Func>
+        typename std::enable_if<
+            std::is_same<typename function_traits<Func>::ret_type,
+                         promise_t>::value>::type
+        gen_on_rejected(Func on_rejected, const promise_t &npm, function<void()> &ret) {
+            ret = [this, on_rejected, npm]() {
+                on_rejected(reason).then_any(
+                    [npm] (pm_any_t result_) {
                         npm.resolve(result_);
                         return none;
-                    }),
-                    function<None(pm_any_t)>([npm] (pm_any_t reason_) {
+                    },
+                    [npm] (pm_any_t reason_) {
                         npm.reject(reason_);
                         return none;
-                    }));
+                    });
             };
         }
 
-        function<void()> gen_on_rejected(
-                function<pm_any_t(pm_any_t)> on_rejected,
-                const promise_t &npm) {
-            return [this, on_rejected, npm]() {
+        template<typename Func>
+        typename std::enable_if<
+            std::is_same<typename function_traits<Func>::ret_type,
+                         pm_any_t>::value>::type
+        gen_on_rejected(Func on_rejected, const promise_t &npm, function<void()> &ret) {
+            ret = [this, on_rejected, npm]() {
                 npm.reject(on_rejected(reason));
             };
         }
@@ -156,40 +178,51 @@ namespace promise {
             //printf("%lx freed\n", (uintptr_t)this);
         }
 
-        template<typename OnFulfilled, typename OnRejected>
-        promise_t then(function<OnFulfilled(pm_any_t)> on_fulfilled,
-                      function<OnRejected(pm_any_t)> on_rejected) {
+        template<typename FuncFulfilled, typename FuncRejected>
+        promise_t then(FuncFulfilled on_fulfilled,
+                      FuncRejected on_rejected) {
             switch (state)
             {
                 case State::Pending:
                     return promise_t([this, on_fulfilled, on_rejected](promise_t npm) {
-                        add_on_fulfilled(gen_on_fulfilled(on_fulfilled, npm));
-                        add_on_rejected(gen_on_rejected(on_rejected, npm));
+                        function<void()> ret;
+                        gen_on_fulfilled(on_fulfilled, npm, ret);
+                        add_on_fulfilled(ret);
+                        gen_on_rejected(on_rejected, npm, ret);
+                        add_on_rejected(ret);
                     });
                 case State::Fulfilled:
                     return promise_t([this, on_fulfilled](promise_t npm) {
-                        gen_on_fulfilled(on_fulfilled, npm)();
+                        function<void()> ret;
+                        gen_on_fulfilled(on_fulfilled, npm, ret);
+                        ret();
                     });
                 case State::Rejected:
                     return promise_t([this, on_rejected](promise_t npm) {
-                        gen_on_rejected(on_rejected, npm)();
+                        function<void()> ret;
+                        gen_on_rejected(on_rejected, npm, ret);
+                        ret();
                     });
                 default: PROMISE_ERR_INVALID_STATE;
             }
         }
 
-        template<typename OnFulfilled>
-        promise_t then(function<OnFulfilled(pm_any_t)> on_fulfilled) {
+        template<typename FuncFulfilled>
+        promise_t then(FuncFulfilled on_fulfilled) {
             switch (state)
             {
                 case State::Pending:
                     return promise_t([this, on_fulfilled](promise_t npm) {
-                        add_on_fulfilled(gen_on_fulfilled(on_fulfilled, npm));
+                        function<void()> ret;
+                        gen_on_fulfilled(on_fulfilled, npm, ret);
+                        add_on_fulfilled(ret);
                         add_on_rejected([this, npm]() {npm.reject(reason);});
                     });
                 case State::Fulfilled:
                     return promise_t([this, on_fulfilled](promise_t npm) {
-                        gen_on_fulfilled(on_fulfilled, npm)();
+                        function<void()> ret;
+                        gen_on_fulfilled(on_fulfilled, npm, ret);
+                        ret();
                     });
                 case State::Rejected:
                     return promise_t([this](promise_t npm) {npm.reject(reason);});
@@ -197,20 +230,24 @@ namespace promise {
             }
         }
  
-        template<typename OnRejected>
-        promise_t fail(function<OnRejected(pm_any_t)> on_rejected) {
+        template<typename FuncRejected>
+        promise_t fail(FuncRejected on_rejected) {
             switch (state)
             {
                 case State::Pending:
                     return promise_t([this, on_rejected](promise_t npm) {
-                        add_on_rejected(gen_on_rejected(on_rejected, npm));
+                        function<void()> ret;
+                        gen_on_rejected(on_rejected, npm, ret);
+                        add_on_rejected(ret);
                         add_on_fulfilled([this, npm]() {npm.resolve(result);});
                     });
                 case State::Fulfilled:
                     return promise_t([this](promise_t npm) {npm.resolve(result);});
                 case State::Rejected:
                     return promise_t([this, on_rejected](promise_t npm) {
-                        add_on_rejected(gen_on_rejected(on_rejected, npm));
+                        function<void()> ret;
+                        gen_on_rejected(on_rejected, npm, ret);
+                        ret();
                     });
                 default: PROMISE_ERR_INVALID_STATE;
             }
@@ -224,6 +261,7 @@ namespace promise {
                     state = State::Fulfilled;
                     //fulfilled_callback();
                     for (const auto &cb: fulfilled_callbacks) cb();
+                    rejected_callbacks.clear();
                     break;
                 default:
                     break;
@@ -238,6 +276,7 @@ namespace promise {
                     state = State::Rejected;
                     //rejected_callback();
                     for (const auto &cb: rejected_callbacks) cb();
+                    rejected_callbacks.clear();
                     break;
                 default:
                     break;
@@ -253,17 +292,17 @@ namespace promise {
         return promise_t([=] (promise_t npm) {
             size_t idx = 0;
             for (const auto &pm: promise_list) {
-                pm.then(function<pm_any_t(pm_any_t)>(
+                pm.then_any(
                     [results, size, idx, npm](pm_any_t result) {
                         (*results)[idx] = result;
                         if (!--(*size))
                             npm.resolve(*results);
-                        return none;
-                    }), function<pm_any_t(pm_any_t)>(
+                        return pm_any_t(none);
+                    },
                     [npm, size](pm_any_t reason) {
                         npm.reject(reason);
-                        return none;
-                    }));
+                        return pm_any_t(none);
+                    });
                 idx++;
             }
         });
@@ -275,19 +314,19 @@ namespace promise {
     template<typename T>
     inline void promise_t::reject(T reason) const { ptr->reject(reason); }
 
-    template<typename F_, typename F, typename R_, typename R>
-    inline promise_t promise_t::then(function<F_(pm_any_t)> fulfilled_callback,
-                                function<R_(pm_any_t)> rejected_callback) const {
+    template<typename FuncFulfilled, typename FuncRejected>
+    inline promise_t promise_t::then_any(FuncFulfilled fulfilled_callback,
+                                    FuncRejected rejected_callback) const {
         return ptr->then(fulfilled_callback, rejected_callback);
     }
 
-    template<typename F_, typename F>
-    inline promise_t promise_t::then(function<F_(pm_any_t)> fulfilled_callback) const {
+    template<typename FuncFulfilled>
+    inline promise_t promise_t::then_any(FuncFulfilled fulfilled_callback) const {
         return ptr->then(fulfilled_callback);
     }
 
-    template<typename R_, typename R>
-    inline promise_t promise_t::fail(function<R_(pm_any_t)> rejected_callback) const {
+    template<typename FuncRejected>
+    inline promise_t promise_t::fail_any(FuncRejected rejected_callback) const {
         return ptr->fail(rejected_callback);
     }
 
@@ -301,44 +340,54 @@ namespace promise {
         using type = promise_t;
     };
 
-    template<typename F_, typename F>
-    inline promise_t promise_t::then(function<F_(F)> on_fulfilled) const {
-        using ret_type = typename callback_type_conversion<F_>::type;
-        return ptr->then(function<ret_type(pm_any_t)>(
+    template<typename T>
+    struct callback_types {
+        using arg_type = typename function_traits<T>::arg_type;
+        using ret_type = typename callback_type_conversion<typename function_traits<T>::ret_type>::type;
+    };
+
+    template<typename FuncFulfilled>
+    inline promise_t promise_t::then(FuncFulfilled on_fulfilled) const {
+        using arg_type = typename callback_types<FuncFulfilled>::arg_type;
+        using ret_type = typename callback_types<FuncFulfilled>::ret_type;
+        return ptr->then(
             [on_fulfilled](pm_any_t _result) {
                 try {
-                    return ret_type(on_fulfilled(std::any_cast<F>(_result)));
+                    return ret_type(on_fulfilled(std::any_cast<arg_type>(_result)));
                 } catch (std::bad_any_cast e) { PROMISE_ERR_MISMATCH_TYPE; }
-            }));
+            });
     }
 
-    template<typename F_, typename F, typename R_, typename R>
-    inline promise_t promise_t::then(function<F_(F)> on_fulfilled,
-                                    function<R_(R)> on_rejected) const {
-        using fulfill_ret_type = typename callback_type_conversion<F_>::type;
-        using reject_ret_type = typename callback_type_conversion<R_>::type;
-        return ptr->then(function<fulfill_ret_type(pm_any_t)>(
+    template<typename FuncFulfilled, typename FuncRejected>
+    inline promise_t promise_t::then(FuncFulfilled on_fulfilled,
+                                    FuncRejected on_rejected) const {
+        using fulfill_arg_type = typename callback_types<FuncFulfilled>::arg_type;
+        using fulfill_ret_type = typename callback_types<FuncFulfilled>::ret_type;
+        using reject_arg_type = typename callback_types<FuncRejected>::arg_type;
+        using reject_ret_type = typename callback_types<FuncRejected>::ret_type;
+        return ptr->then(
             [on_fulfilled](pm_any_t _result) {
                 try {
-                    return fulfill_ret_type(on_fulfilled(std::any_cast<F>(_result)));
+                    return fulfill_ret_type(on_fulfilled(std::any_cast<fulfill_arg_type>(_result)));
                 } catch (std::bad_any_cast e) { PROMISE_ERR_MISMATCH_TYPE; }
-            }), function<fulfill_ret_type(pm_any_t)>(
+            },
             [on_rejected](pm_any_t _reason) {
                 try {
-                    return reject_ret_type(on_rejected(std::any_cast<R>(_reason)));
+                    return reject_ret_type(on_rejected(std::any_cast<reject_arg_type>(_reason)));
                 } catch (std::bad_any_cast e) { PROMISE_ERR_MISMATCH_TYPE; }
-            }));
+            });
     }
 
-    template<typename R_, typename R>
-    inline promise_t promise_t::fail(function<R_(R)> on_rejected) const {
-        using ret_type = typename callback_type_conversion<R_>::type;
-        return ptr->fail(function<ret_type(pm_any_t)>(
+    template<typename FuncRejected>
+    inline promise_t promise_t::fail(FuncRejected on_rejected) const {
+        using arg_type = typename callback_types<FuncRejected>::arg_type;
+        using ret_type = typename callback_types<FuncRejected>::ret_type;
+        return ptr->fail(
             [on_rejected](pm_any_t _reason) {
                 try {
-                    return ret_type(on_rejected(std::any_cast<R>(_reason)));
+                    return ret_type(on_rejected(std::any_cast<arg_type>(_reason)));
                 } catch (std::bad_any_cast e) { PROMISE_ERR_MISMATCH_TYPE; }
-            }));
+            });
     }
 }
 #endif
diff --git a/test.cpp b/test.cpp
index 327f5a6..2719340 100644
--- a/test.cpp
+++ b/test.cpp
@@ -12,25 +12,26 @@ int main() {
         puts("pm1");
         //t1 = [pm]() {pm.reject(5);};
         t1 = [pm]() {pm.resolve(5);};
-    }).then(std::function<int(int)>([](int x) {
+    }).then([](int x) {
         printf("%d\n", x);
         return 6;
-    })).then(std::function<int(int)>([](int y) {
+    }).then([](int y) {
         printf("%d\n", y);
         return 0;
-    })).then(std::function<promise_t(int)>([&t2](int x) {
+    }).then([&t2](int x) {
         auto pm2 = promise_t([x, &t2](promise_t pm2) {
             printf("pm2 %d\n", x);
             t2 = [pm2]() {pm2.resolve(std::string("hello"));};
         });
         return pm2;
-    })).then(std::function<int(std::string)>([](std::string s) {
+    }).then([](std::string s) {
         printf("%s\n", s.c_str());
         return 10;
-    })).then(std::function<promise::None(int)>([](int x) {
+    }).then([](int x) {
         printf("%d\n", x);
         return promise::none;
-    }));
+    });
+    
     auto p1 = promise_t([&t4](promise_t pm) {
         puts("p1");
         t4 = [pm]() {pm.resolve(1);};
@@ -47,25 +48,22 @@ int main() {
     });
 
     auto p4 = promise::all(std::vector<promise_t>{p1, p2, p3})
-        .then(std::function<int(promise::values_t)>(
-            [](const promise::values_t values) {
+        .then([](const promise::values_t values) {
             printf("%d %s %s\n", std::any_cast<int>(values[0]),
                                 std::any_cast<std::string>(values[1]).c_str(),
                                 std::any_cast<std::string>(values[2]).c_str());
-        return 100;
-    }));
+            return 100;
+        });
 
     auto p5 = promise::all(std::vector<promise_t>{pm, p4})
-        .fail(std::function<int(int)>(
-            [](int reason) {
-                printf("reason: %d\n", reason);
-                return reason;
-        }))
-        .then(std::function<promise::None(promise::values_t)>(
-            [](const promise::values_t values) {
-                printf("finally %d\n", std::any_cast<int>(values[1]));
-                return promise::none;
-        }));
+        .fail([](int reason) {
+            printf("reason: %d\n", reason);
+            return reason;
+        })
+        .then([](const promise::values_t values) {
+            printf("finally %d\n", std::any_cast<int>(values[1]));
+            return promise::none;
+        });
     puts("calling t");
     t4();
     puts("calling t2");
-- 
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