From f859ae88d9a306a12d0fe552a9ac3b3f2d26e22f Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sun, 1 Apr 2018 14:21:59 +0100
Subject: Simplify by replacing enable_if with if constexpr

---
 libdbpp/column.cpp               | 19 ++++++++-----------
 libdbpp/selectcommandUtil.impl.h | 21 ++++++++++-----------
 libdbpp/testCore.cpp             | 19 ++++++++-----------
 3 files changed, 26 insertions(+), 33 deletions(-)

diff --git a/libdbpp/column.cpp b/libdbpp/column.cpp
index f8eae65..b660cd3 100644
--- a/libdbpp/column.cpp
+++ b/libdbpp/column.cpp
@@ -1,5 +1,4 @@
 #include "column.h"
-#include <boost/utility/enable_if.hpp>
 #include <exception>
 #include <compileTimeFormatter.h>
 
@@ -43,16 +42,14 @@ class Extract : public DB::HandleField {
 		void blob(const Blob & v) override { (*this)(v); }
 		void null() override { }
 
-		template <typename D, typename dummy = int>
-		void operator()(const D &,
-				typename boost::disable_if<std::is_convertible<D, T>, dummy>::type = 0) {
-			throw InvalidConversion(typeid(D).name(), typeid(T).name());
-		}
-
-		template <typename D, typename dummy = int>
-		void operator()(const D & v,
-				typename boost::enable_if<std::is_convertible<D, T>, dummy>::type = 0) {
-			target = (T)v;
+		template <typename D>
+		void operator()(const D & v) {
+			if constexpr (std::is_convertible<D, T>::value) {
+				target = (T)v;
+			}
+			else {
+				throw InvalidConversion(typeid(D).name(), typeid(T).name());
+			}
 		}
 
 		T & target;
diff --git a/libdbpp/selectcommandUtil.impl.h b/libdbpp/selectcommandUtil.impl.h
index dfe6894..6446de0 100644
--- a/libdbpp/selectcommandUtil.impl.h
+++ b/libdbpp/selectcommandUtil.impl.h
@@ -6,20 +6,19 @@
 
 /// @cond
 namespace DB {
-	template<typename Fields, typename Func, unsigned int field, typename ... Fn>
-	inline typename std::enable_if<field >= std::tuple_size<Fields>::value>::type
-	forEachField(DB::SelectCommand *, const Func & func, const Fn & ... args)
-	{
-		func(args...);
-	}
-
 	template<typename Fields, typename Func, unsigned int field, typename ... Fn, typename ... Args>
-	inline typename std::enable_if<field < std::tuple_size<Fields>::value>::type
+	inline void
 	forEachField(DB::SelectCommand * sel, const Func & func, const Args & ... args)
 	{
-		typename std::tuple_element<field, Fields>::type a;
-		(*sel)[field] >> a;
-		forEachField<Fields, Func, field + 1, Fn...>(sel, func, args..., a);
+		if constexpr (field >= std::tuple_size<Fields>::value) {
+			(void)sel;
+			func(args...);
+		}
+		else {
+			typename std::tuple_element<field, Fields>::type a;
+			(*sel)[field] >> a;
+			forEachField<Fields, Func, field + 1, Fn...>(sel, func, args..., a);
+		}
 	}
 
 	template<typename ... Fn, typename Func>
diff --git a/libdbpp/testCore.cpp b/libdbpp/testCore.cpp
index 890cb18..b55d16d 100644
--- a/libdbpp/testCore.cpp
+++ b/libdbpp/testCore.cpp
@@ -2,7 +2,6 @@
 #include <selectcommand.h>
 #include <boost/date_time/posix_time/posix_time.hpp>
 #include <boost/test/test_tools.hpp>
-#include <boost/utility/enable_if.hpp>
 #include <compileTimeFormatter.h>
 
 namespace DB {
@@ -31,16 +30,14 @@ class Assert : public DB::HandleField {
 		void blob(const Blob & v) override { (*this)(v); }
 		void null() override { }
 
-		template <typename D, typename dummy = int>
-		void operator()(const D &,
-				typename boost::disable_if<std::is_convertible<D, T>, dummy>::type = 0) {
-			BOOST_ERROR("Unexpected column type " << typeid(D).name());
-		}
-
-		template <typename D, typename dummy = int>
-		void operator()(const D & v,
-				typename boost::enable_if<std::is_convertible<D, T>, dummy>::type = 0) {
-			BOOST_REQUIRE_EQUAL(expected, v);
+		template <typename D>
+		void operator()(const D & v) {
+			if constexpr (std::is_convertible<D, T>::value) {
+				BOOST_REQUIRE_EQUAL(expected, v);
+			}
+			else {
+				BOOST_ERROR("Unexpected column type " << typeid(D).name());
+			}
 		}
 
 		const T & expected;
-- 
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