Added if_m

Author: polytypic

internals/testing/compile_only_test.cpp

@@ -48,4 +48,10 @@ static_assert(!is_stored_plain_v<char *>);
 static_assert(is_stored_plain_v<int *>);
 static_assert(is_stored_plain_v<int * [2]>);
 
+static_assert(lax::value_of_v<lax::if_m<lax::and_m<>, lax::value_t<int, 1>,
+                                        lax::value_t<int, 2>>> == 1);
+
+static_assert(lax::value_of_v<lax::if_m<lax::or_m<>, lax::value_t<int, 1>,
+                                        lax::value_t<int, 2>>> == 2);
+
 int main() { return 0; }

provides/include/lax_v1/logical.hpp

@@ -4,6 +4,16 @@
 #include "lax_v1/logical_synopsis.hpp"
 #include "lax_v1/value.hpp"
 
+template <class ElseExpr> struct lax_v1::if_m<ElseExpr> : force_t<ElseExpr> {};
+template <class CondExpr, class ThenExpr, class... ElseExprs>
+struct lax_v1::if_m<CondExpr, ThenExpr, ElseExprs...>
+    : if_m<force_t<CondExpr>, ThenExpr, ElseExprs...> {};
+template <class ThenExpr, class... ElseExprs>
+struct lax_v1::if_m<lax_v1::true_t, ThenExpr, ElseExprs...> : ThenExpr {};
+template <class ThenExpr, class... ElseExprs>
+struct lax_v1::if_m<lax_v1::false_t, ThenExpr, ElseExprs...>
+    : if_m<ElseExprs...> {};
+
 template <> struct lax_v1::and_m<> : true_t {};
 template <class... Exprs>
 struct lax_v1::and_m<lax_v1::false_t, Exprs...> : false_t {};

provides/include/lax_v1/logical_synopsis.hpp

@@ -2,6 +2,8 @@
 
 namespace lax_v1 {
 
+template <class... Exprs> struct if_m;
+
 template <class... Exprs> struct and_m;
 
 template <class Expr> struct not_m;