diff --git a/include/boost/histogram/algorithm/reduce.hpp b/include/boost/histogram/algorithm/reduce.hpp
index f3a025aa..a9d6c024 100644
--- a/include/boost/histogram/algorithm/reduce.hpp
+++ b/include/boost/histogram/algorithm/reduce.hpp
@@ -10,10 +10,8 @@
 #include <boost/assert.hpp>
 #include <boost/histogram/axis/traits.hpp>
 #include <boost/histogram/detail/axes.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <boost/histogram/detail/make_default.hpp>
 #include <boost/histogram/detail/static_if.hpp>
-#include <boost/histogram/detail/type_name.hpp>
 #include <boost/histogram/fwd.hpp>
 #include <boost/histogram/indexed.hpp>
 #include <boost/histogram/unsafe_access.hpp>
@@ -21,6 +19,7 @@
 #include <cmath>
 #include <initializer_list>
 #include <stdexcept>
+#include <string>
 
 namespace boost {
 namespace histogram {
@@ -250,10 +249,9 @@ decltype(auto) reduce(const Histogram& hist, const Iterable& options) {
             o.end -= (o.end - o.begin) % o.merge;
             aout = A(ain, o.begin, o.end, o.merge);
           },
-          [](auto&&, const auto& ain) {
-            using A = std::decay_t<decltype(ain)>;
-            BOOST_THROW_EXCEPTION(std::invalid_argument(
-                detail::cat(detail::type_name<A>(), " is not reducible")));
+          [iaxis](auto&&, const auto&) {
+            BOOST_THROW_EXCEPTION(std::invalid_argument("axis " + std::to_string(iaxis) +
+                                                        " is not reducible"));
           },
           axis::get<A>(detail::axis_get(axes, iaxis)), a);
     } else {
diff --git a/include/boost/histogram/axis/ostream.hpp b/include/boost/histogram/axis/ostream.hpp
index f9de9010..ca307a59 100644
--- a/include/boost/histogram/axis/ostream.hpp
+++ b/include/boost/histogram/axis/ostream.hpp
@@ -11,13 +11,13 @@
 
 #include <boost/assert.hpp>
 #include <boost/histogram/axis/regular.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <boost/histogram/detail/static_if.hpp>
 #include <boost/histogram/detail/type_name.hpp>
 #include <boost/histogram/fwd.hpp>
 #include <boost/throw_exception.hpp>
 #include <iomanip>
 #include <iosfwd>
+#include <sstream>
 #include <stdexcept>
 #include <type_traits>
 
diff --git a/include/boost/histogram/axis/traits.hpp b/include/boost/histogram/axis/traits.hpp
index 8502c518..62a8afe9 100644
--- a/include/boost/histogram/axis/traits.hpp
+++ b/include/boost/histogram/axis/traits.hpp
@@ -10,7 +10,6 @@
 #include <boost/core/ignore_unused.hpp>
 #include <boost/histogram/axis/option.hpp>
 #include <boost/histogram/detail/args_type.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <boost/histogram/detail/detect.hpp>
 #include <boost/histogram/detail/static_if.hpp>
 #include <boost/histogram/detail/try_cast.hpp>
@@ -22,6 +21,7 @@
 #include <boost/throw_exception.hpp>
 #include <boost/variant2/variant.hpp>
 #include <stdexcept>
+#include <string>
 #include <utility>
 
 namespace boost {
@@ -56,7 +56,7 @@ double value_method_switch_impl1(std::false_type, I&&, D&&, const A&) {
   // comma trick to make all compilers happy; some would complain about
   // unreachable code after the throw, others about a missing return
   return BOOST_THROW_EXCEPTION(
-             std::runtime_error(cat(type_name<A>(), " has no value method"))),
+             std::runtime_error(type_name<A>() + " has no value method")),
          double{};
 }
 
diff --git a/include/boost/histogram/axis/variable.hpp b/include/boost/histogram/axis/variable.hpp
index 46feb0ad..53af4416 100644
--- a/include/boost/histogram/axis/variable.hpp
+++ b/include/boost/histogram/axis/variable.hpp
@@ -83,12 +83,14 @@ public:
 
     vec_.reserve(std::distance(begin, end));
     vec_.emplace_back(*begin++);
+    bool strictly_ascending = true;
     while (begin != end) {
-      if (*begin <= vec_.back())
-        BOOST_THROW_EXCEPTION(
-            std::invalid_argument("input sequence must be strictly ascending"));
+      if (*begin <= vec_.back()) strictly_ascending = false;
       vec_.emplace_back(*begin++);
     }
+    if (!strictly_ascending)
+      BOOST_THROW_EXCEPTION(
+          std::invalid_argument("input sequence must be strictly ascending"));
   }
 
   /** Construct variable axis from iterable range of bin edges.
diff --git a/include/boost/histogram/axis/variant.hpp b/include/boost/histogram/axis/variant.hpp
index 1a3db038..949ec5c6 100644
--- a/include/boost/histogram/axis/variant.hpp
+++ b/include/boost/histogram/axis/variant.hpp
@@ -11,7 +11,6 @@
 #include <boost/histogram/axis/iterator.hpp>
 #include <boost/histogram/axis/polymorphic_bin.hpp>
 #include <boost/histogram/axis/traits.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <boost/histogram/detail/relaxed_equal.hpp>
 #include <boost/histogram/detail/static_if.hpp>
 #include <boost/histogram/detail/type_name.hpp>
@@ -20,7 +19,6 @@
 #include <boost/mp11/list.hpp>      // mp_first
 #include <boost/throw_exception.hpp>
 #include <boost/variant2/variant.hpp>
-#include <ostream>
 #include <stdexcept>
 #include <type_traits>
 #include <utility>
@@ -74,9 +72,9 @@ public:
           detail::static_if<is_bounded_type<U>>(
               [this](const auto& u) { this->operator=(u); },
               [](const auto&) {
-                BOOST_THROW_EXCEPTION(std::runtime_error(detail::cat(
-                    detail::type_name<U>(), " is not convertible to a bounded type of ",
-                    detail::type_name<variant>())));
+                BOOST_THROW_EXCEPTION(std::runtime_error(
+                    detail::type_name<U>() + " is not convertible to a bounded type of " +
+                    detail::type_name<variant>()));
               },
               u);
         },
@@ -109,11 +107,11 @@ public:
               [](const auto& a) -> const metadata_type& { return traits::metadata(a); },
               [](const auto&) -> const metadata_type& {
                 BOOST_THROW_EXCEPTION(std::runtime_error(
-                    detail::cat("cannot return metadata of type ", detail::type_name<M>(),
-                                " through axis::variant interface which uses type ",
-                                detail::type_name<metadata_type>(),
-                                "; use boost::histogram::axis::get to obtain a reference "
-                                "of this axis type")));
+                    "cannot return metadata of type " + detail::type_name<M>() +
+                    " through axis::variant interface which uses type " +
+                    detail::type_name<metadata_type>() +
+                    "; use boost::histogram::axis::get to obtain a reference "
+                    "of this axis type"));
               },
               a);
         },
@@ -130,11 +128,11 @@ public:
               [](auto& a) -> metadata_type& { return traits::metadata(a); },
               [](auto&) -> metadata_type& {
                 BOOST_THROW_EXCEPTION(std::runtime_error(
-                    detail::cat("cannot return metadata of type ", detail::type_name<M>(),
-                                " through axis::variant interface which uses type ",
-                                detail::type_name<metadata_type>(),
-                                "; use boost::histogram::axis::get to obtain a reference "
-                                "of this axis type")));
+                    "cannot return metadata of type " + detail::type_name<M>() +
+                    " through axis::variant interface which uses type " +
+                    detail::type_name<metadata_type>() +
+                    "; use boost::histogram::axis::get to obtain a reference "
+                    "of this axis type"));
               },
               a);
         },
diff --git a/include/boost/histogram/detail/axes.hpp b/include/boost/histogram/detail/axes.hpp
index 018e648c..e973b416 100644
--- a/include/boost/histogram/detail/axes.hpp
+++ b/include/boost/histogram/detail/axes.hpp
@@ -22,6 +22,7 @@
 #include <boost/mp11/utility.hpp>
 #include <boost/throw_exception.hpp>
 #include <stdexcept>
+#include <string>
 #include <tuple>
 #include <type_traits>
 
@@ -57,9 +58,10 @@ template <class T>
 void throw_if_axes_is_too_large(const T& axes) {
   if (axes_rank(axes) > BOOST_HISTOGRAM_DETAIL_AXES_LIMIT)
     BOOST_THROW_EXCEPTION(
-        std::invalid_argument(cat("length of axis vector exceeds internal buffers, "
-                                  "recompile with -DBOOST_HISTOGRAM_DETAIL_AXES_LIMIT=",
-                                  axes_rank(axes), " to increase internal buffers")));
+        std::invalid_argument("length of axis vector exceeds internal buffers, "
+                              "recompile with "
+                              "-DBOOST_HISTOGRAM_DETAIL_AXES_LIMIT=<new max size> "
+                              "to increase internal buffers"));
 }
 
 // tuple is never too large because internal buffers adapt to size of tuple
diff --git a/include/boost/histogram/detail/cat.hpp b/include/boost/histogram/detail/cat.hpp
deleted file mode 100644
index f977c014..00000000
--- a/include/boost/histogram/detail/cat.hpp
+++ /dev/null
@@ -1,34 +0,0 @@
-// Copyright 2015-2017 Hans Dembinski
-//
-// Distributed under the Boost Software License, Version 1.0.
-// (See accompanying file LICENSE_1_0.txt
-// or copy at http://www.boost.org/LICENSE_1_0.txt)
-
-#ifndef BOOST_HISTOGRAM_DETAIL_CAT_HPP
-#define BOOST_HISTOGRAM_DETAIL_CAT_HPP
-
-#include <boost/config.hpp>
-#include <sstream>
-
-namespace boost {
-namespace histogram {
-namespace detail {
-BOOST_ATTRIBUTE_UNUSED inline void cat_impl(std::ostringstream&) {}
-
-template <typename T, typename... Ts>
-void cat_impl(std::ostringstream& os, const T& t, const Ts&... ts) {
-  os << t;
-  cat_impl(os, ts...);
-}
-
-template <typename... Ts>
-std::string cat(const Ts&... args) {
-  std::ostringstream os;
-  cat_impl(os, args...);
-  return os.str();
-}
-} // namespace detail
-} // namespace histogram
-} // namespace boost
-
-#endif
diff --git a/include/boost/histogram/detail/try_cast.hpp b/include/boost/histogram/detail/try_cast.hpp
index 249f4e03..1e8a7d27 100644
--- a/include/boost/histogram/detail/try_cast.hpp
+++ b/include/boost/histogram/detail/try_cast.hpp
@@ -9,11 +9,11 @@
 
 #include <boost/config.hpp>
 #include <boost/core/demangle.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <boost/histogram/detail/type_name.hpp>
 #include <boost/mp11/integral.hpp>
 #include <boost/throw_exception.hpp>
 #include <stdexcept>
+#include <string>
 #include <type_traits>
 
 namespace boost {
@@ -21,7 +21,7 @@ namespace histogram {
 namespace detail {
 template <class T, class E, class U>
 BOOST_NORETURN T try_cast_impl(mp11::mp_int<0>, U&&) {
-  BOOST_THROW_EXCEPTION(E(cat("cannot cast ", type_name<T>(), " to ", type_name<U>())));
+  BOOST_THROW_EXCEPTION(E("cannot cast " + type_name<T>() + " to " + type_name<U>()));
 }
 
 template <class T, class E, class U>
diff --git a/include/boost/histogram/detail/type_name.hpp b/include/boost/histogram/detail/type_name.hpp
index 25950bca..bea8f88a 100644
--- a/include/boost/histogram/detail/type_name.hpp
+++ b/include/boost/histogram/detail/type_name.hpp
@@ -9,7 +9,6 @@
 
 #include <boost/core/typeinfo.hpp>
 #include <boost/type.hpp>
-#include <sstream>
 #include <string>
 
 namespace boost {
@@ -17,31 +16,28 @@ namespace histogram {
 namespace detail {
 
 template <class T>
-std::ostream& type_name_impl(std::ostream& os, boost::type<T>) {
-  os << boost::core::demangled_name(BOOST_CORE_TYPEID(T));
-  return os;
+std::string type_name_impl(boost::type<T>) {
+  return boost::core::demangled_name(BOOST_CORE_TYPEID(T));
 }
 
 template <class T>
-std::ostream& type_name_impl(std::ostream& os, boost::type<const T>) {
-  return type_name_impl(os, boost::type<T>{}) << " const";
+std::string type_name_impl(boost::type<const T>) {
+  return type_name_impl(boost::type<T>{}) + " const";
 }
 
 template <class T>
-std::ostream& type_name_impl(std::ostream& os, boost::type<T&>) {
-  return type_name_impl(os, boost::type<T>{}) << "&";
+std::string type_name_impl(boost::type<T&>) {
+  return type_name_impl(boost::type<T>{}) + " &";
 }
 
 template <class T>
-std::ostream& type_name_impl(std::ostream& os, boost::type<T&&>) {
-  return type_name_impl(os, boost::type<T>{}) << "&&";
+std::string type_name_impl(boost::type<T&&>) {
+  return type_name_impl(boost::type<T>{}) + " &&";
 }
 
 template <class T>
 std::string type_name() {
-  std::ostringstream os;
-  type_name_impl(os, boost::type<T>{});
-  return os.str();
+  return type_name_impl(boost::type<T>{});
 }
 
 } // namespace detail
diff --git a/include/boost/histogram/storage_adaptor.hpp b/include/boost/histogram/storage_adaptor.hpp
index e4c849bc..b704526f 100644
--- a/include/boost/histogram/storage_adaptor.hpp
+++ b/include/boost/histogram/storage_adaptor.hpp
@@ -10,7 +10,6 @@
 #include <algorithm>
 #include <boost/core/nvp.hpp>
 #include <boost/histogram/detail/array_wrapper.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <boost/histogram/detail/detect.hpp>
 #include <boost/histogram/detail/iterator_adaptor.hpp>
 #include <boost/histogram/detail/safe_comparison.hpp>
@@ -90,20 +89,19 @@ struct array_impl : T {
 
   template <class U, class = requires_iterable<U>>
   array_impl& operator=(const U& u) {
+    if (u.size() > T::max_size()) // for std::arra
+      BOOST_THROW_EXCEPTION(std::length_error("argument size exceeds maximum capacity"));
     size_ = u.size();
-    if (size_ > T::max_size()) // for std::array
-      BOOST_THROW_EXCEPTION(std::length_error(
-          detail::cat("size ", size_, " exceeds maximum capacity ", T::max_size())));
-    auto it = T::begin();
-    for (auto&& x : u) *it++ = x;
+    using std::begin;
+    using std::end;
+    std::copy(begin(u), end(u), T::begin());
     return *this;
   }
 
   void reset(std::size_t n) {
     using value_type = typename T::value_type;
     if (n > T::max_size()) // for std::array
-      BOOST_THROW_EXCEPTION(std::length_error(
-          detail::cat("size ", n, " exceeds maximum capacity ", T::max_size())));
+      BOOST_THROW_EXCEPTION(std::length_error("argument size exceeds maximum capacity"));
     std::fill_n(T::begin(), n, value_type());
     size_ = n;
   }
diff --git a/test/axis_category_test.cpp b/test/axis_category_test.cpp
index 11c9db90..5afe477c 100644
--- a/test/axis_category_test.cpp
+++ b/test/axis_category_test.cpp
@@ -9,7 +9,6 @@
 #include <boost/histogram/axis/category.hpp>
 #include <boost/histogram/axis/ostream.hpp>
 #include <boost/histogram/axis/traits.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <limits>
 #include <sstream>
 #include <string>
@@ -17,10 +16,11 @@
 #include "std_ostream.hpp"
 #include "throw_exception.hpp"
 #include "utility_axis.hpp"
-
-using namespace boost::histogram;
+#include "utility_str.hpp"
 
 int main() {
+  using namespace boost::histogram;
+
   BOOST_TEST(std::is_nothrow_move_constructible<axis::category<int>>::value);
   BOOST_TEST(std::is_nothrow_move_constructible<axis::category<std::string>>::value);
   BOOST_TEST(std::is_nothrow_move_assignable<axis::category<int>>::value);
@@ -69,7 +69,7 @@ int main() {
     BOOST_TEST_EQ(a.value(2), C);
     BOOST_TEST_THROWS(a.value(3), std::out_of_range);
 
-    BOOST_TEST_EQ(detail::cat(a),
+    BOOST_TEST_EQ(str(a),
                   "category(\"A\", \"B\", \"C\", metadata=\"bar\", options=overflow)");
   }
 
@@ -131,7 +131,7 @@ int main() {
     BOOST_TEST_EQ(a.update(10), std::make_pair(2, 0));
     BOOST_TEST_EQ(a.size(), 3);
 
-    BOOST_TEST_EQ(detail::cat(a), "category(5, 1, 10, options=growth)");
+    BOOST_TEST_EQ(str(a), "category(5, 1, 10, options=growth)");
   }
 
   // iterators
diff --git a/test/axis_integer_test.cpp b/test/axis_integer_test.cpp
index 10c6b68f..d3556f41 100644
--- a/test/axis_integer_test.cpp
+++ b/test/axis_integer_test.cpp
@@ -7,16 +7,17 @@
 #include <boost/core/lightweight_test.hpp>
 #include <boost/histogram/axis/integer.hpp>
 #include <boost/histogram/axis/ostream.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <limits>
+#include <sstream>
 #include <type_traits>
 #include "std_ostream.hpp"
 #include "throw_exception.hpp"
 #include "utility_axis.hpp"
-
-using namespace boost::histogram;
+#include "utility_str.hpp"
 
 int main() {
+  using namespace boost::histogram;
+
   BOOST_TEST(std::is_nothrow_move_assignable<axis::integer<>>::value);
   BOOST_TEST(std::is_nothrow_move_constructible<axis::integer<>>::value);
 
@@ -44,7 +45,7 @@ int main() {
     BOOST_TEST_EQ(a.index(10), 3);
     BOOST_TEST_EQ(a.index(std::numeric_limits<double>::quiet_NaN()), 3);
 
-    BOOST_TEST_EQ(detail::cat(a),
+    BOOST_TEST_EQ(str(a),
                   "integer(-1, 2, metadata=\"bar\", options=underflow | overflow)");
 
     axis::integer<double> b;
@@ -72,7 +73,7 @@ int main() {
     BOOST_TEST_EQ(a.index(2), 3);
     BOOST_TEST_EQ(a.index(10), 3);
 
-    BOOST_TEST_EQ(detail::cat(a), "integer(-1, 2, options=underflow | overflow)");
+    BOOST_TEST_EQ(str(a), "integer(-1, 2, options=underflow | overflow)");
   }
 
   // axis::integer int,circular
@@ -89,7 +90,7 @@ int main() {
     BOOST_TEST_EQ(a.index(1), 0);
     BOOST_TEST_EQ(a.index(2), 1);
 
-    BOOST_TEST_EQ(detail::cat(a), "integer(-1, 1, options=circular)");
+    BOOST_TEST_EQ(str(a), "integer(-1, 1, options=circular)");
   }
 
   // axis::integer double,circular
diff --git a/test/axis_regular_test.cpp b/test/axis_regular_test.cpp
index 4f52c981..5d3e111c 100644
--- a/test/axis_regular_test.cpp
+++ b/test/axis_regular_test.cpp
@@ -7,7 +7,6 @@
 #include <boost/core/lightweight_test.hpp>
 #include <boost/histogram/axis/ostream.hpp>
 #include <boost/histogram/axis/regular.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <limits>
 #include <sstream>
 #include <type_traits>
@@ -15,12 +14,13 @@
 #include "std_ostream.hpp"
 #include "throw_exception.hpp"
 #include "utility_axis.hpp"
-
-using namespace boost::histogram;
-namespace tr = axis::transform;
-using def = use_default;
+#include "utility_str.hpp"
 
 int main() {
+  using namespace boost::histogram;
+  using def = use_default;
+  namespace tr = axis::transform;
+
   BOOST_TEST(std::is_nothrow_move_assignable<axis::regular<>>::value);
   BOOST_TEST(std::is_nothrow_move_constructible<axis::regular<>>::value);
 
@@ -73,7 +73,7 @@ int main() {
     BOOST_TEST_EQ(a.index(std::numeric_limits<double>::infinity()), 4);
     BOOST_TEST_EQ(a.index(std::numeric_limits<double>::quiet_NaN()), 4);
 
-    BOOST_TEST_EQ(detail::cat(a),
+    BOOST_TEST_EQ(str(a),
                   "regular(4, -2, 2, metadata=\"bar\", options=underflow | overflow)");
   }
 
@@ -116,7 +116,7 @@ int main() {
 
     BOOST_TEST_THROWS((axis::regular<double, tr::log>{2, -1, 0}), std::invalid_argument);
 
-    BOOST_TEST_EQ(detail::cat(a), "regular_log(2, 1, 100, options=underflow | overflow)");
+    BOOST_TEST_EQ(str(a), "regular_log(2, 1, 100, options=underflow | overflow)");
   }
 
   // with sqrt transform
@@ -138,7 +138,7 @@ int main() {
     BOOST_TEST_EQ(a.index(100), 2);
     BOOST_TEST_EQ(a.index(std::numeric_limits<double>::infinity()), 2);
 
-    BOOST_TEST_EQ(detail::cat(a), "regular_sqrt(2, 0, 4, options=underflow | overflow)");
+    BOOST_TEST_EQ(str(a), "regular_sqrt(2, 0, 4, options=underflow | overflow)");
   }
 
   // with pow transform
@@ -160,7 +160,7 @@ int main() {
     BOOST_TEST_EQ(a.index(100), 2);
     BOOST_TEST_EQ(a.index(std::numeric_limits<double>::infinity()), 2);
 
-    BOOST_TEST_EQ(detail::cat(a),
+    BOOST_TEST_EQ(str(a),
                   "regular_pow(2, 0, 4, options=underflow | overflow, power=0.5)");
   }
 
@@ -244,7 +244,7 @@ int main() {
   // null_type streamable
   {
     auto a = axis::regular<float, def, axis::null_type>(2, 0, 1);
-    BOOST_TEST_EQ(detail::cat(a), "regular(2, 0, 1, options=underflow | overflow)");
+    BOOST_TEST_EQ(str(a), "regular(2, 0, 1, options=underflow | overflow)");
   }
 
   // shrink and rebin
diff --git a/test/axis_variable_test.cpp b/test/axis_variable_test.cpp
index 97eb0b39..cb27a093 100644
--- a/test/axis_variable_test.cpp
+++ b/test/axis_variable_test.cpp
@@ -7,14 +7,15 @@
 #include <boost/core/lightweight_test.hpp>
 #include <boost/histogram/axis/ostream.hpp>
 #include <boost/histogram/axis/variable.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <limits>
+#include <sstream>
 #include <type_traits>
 #include <vector>
 #include "is_close.hpp"
 #include "std_ostream.hpp"
 #include "throw_exception.hpp"
 #include "utility_axis.hpp"
+#include "utility_str.hpp"
 
 using namespace boost::histogram;
 
@@ -24,9 +25,9 @@ int main() {
 
   // bad_ctors
   {
-    auto empty = std::vector<double>(0);
-    BOOST_TEST_THROWS((axis::variable<>(empty)), std::invalid_argument);
+    BOOST_TEST_THROWS(axis::variable<>(std::vector<double>{}), std::invalid_argument);
     BOOST_TEST_THROWS(axis::variable<>({1.0}), std::invalid_argument);
+    BOOST_TEST_THROWS(axis::variable<>({1.0, 1.0}), std::invalid_argument);
     BOOST_TEST_THROWS(axis::variable<>({1.0, -1.0}), std::invalid_argument);
   }
 
@@ -54,7 +55,7 @@ int main() {
     BOOST_TEST_EQ(a.index(std::numeric_limits<double>::infinity()), 2);
     BOOST_TEST_EQ(a.index(std::numeric_limits<double>::quiet_NaN()), 2);
 
-    BOOST_TEST_EQ(detail::cat(a),
+    BOOST_TEST_EQ(str(a),
                   "variable(-1, 0, 1, metadata=\"bar\", options=underflow | overflow)");
 
     axis::variable<> b;
diff --git a/test/axis_variant_test.cpp b/test/axis_variant_test.cpp
index 65173f6e..016b592d 100644
--- a/test/axis_variant_test.cpp
+++ b/test/axis_variant_test.cpp
@@ -11,21 +11,22 @@
 #include <boost/histogram/axis/ostream.hpp>
 #include <boost/histogram/axis/regular.hpp>
 #include <boost/histogram/axis/variant.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <boost/histogram/detail/type_name.hpp>
-#include <sstream>
 #include <string>
 #include <type_traits>
 #include <vector>
 #include "throw_exception.hpp"
 #include "utility_allocator.hpp"
 #include "utility_axis.hpp"
-
-using namespace boost::histogram;
-namespace tr = axis::transform;
+#include "utility_str.hpp"
 
 int main() {
-  { (void)axis::variant<>{}; }
+  using namespace boost::histogram;
+  namespace tr = axis::transform;
+
+  {
+    (void)axis::variant<>{};
+  }
 
   {
     using meta_type = std::vector<int>;
@@ -124,15 +125,15 @@ int main() {
     auto test = [](auto&& a, const char* ref) {
       using T = std::decay_t<decltype(a)>;
       axis::variant<T> axis(std::move(a));
-      BOOST_TEST_CSTR_EQ(detail::cat(axis).c_str(), ref);
+      BOOST_TEST_CSTR_EQ(str(axis).c_str(), ref);
     };
 
     test(axis::regular<>(2, -1, 1, "regular1"),
          "regular(2, -1, 1, metadata=\"regular1\", options=underflow | overflow)");
 
     struct user_defined {};
-    const auto ref = detail::cat(
-        "integer(-1, 1, metadata=", detail::type_name<user_defined>(), ", options=none)");
+    const auto ref = "integer(-1, 1, metadata=" + detail::type_name<user_defined>() +
+                     ", options=none)";
     test(axis::integer<int, user_defined, axis::option::none_t>(-1, 1), ref.c_str());
   }
 
@@ -141,7 +142,7 @@ int main() {
     auto test = [](auto&& a, const char* ref) {
       using T = std::decay_t<decltype(a)>;
       axis::variant<T> axis(std::move(a));
-      BOOST_TEST_CSTR_EQ(detail::cat(axis.bin(0)).c_str(), ref);
+      BOOST_TEST_CSTR_EQ(str(axis.bin(0)).c_str(), ref);
     };
 
     test(axis::regular<>(2, 1, 2), "[1, 1.5)");
@@ -190,7 +191,7 @@ int main() {
     BOOST_TEST_EQ(axis.index(9), 1);
     BOOST_TEST_EQ(axis.size(), 2);
     BOOST_TEST_EQ(axis.metadata(), axis::null_type{});
-    BOOST_TEST_CSTR_EQ(detail::cat(axis).c_str(), "<unstreamable>");
+    BOOST_TEST_CSTR_EQ(str(axis).c_str(), "<unstreamable>");
     BOOST_TEST_THROWS(axis.value(0), std::runtime_error);
 
     axis = axis::category<std::string>({"A", "B"}, "category");
diff --git a/test/detail_misc_test.cpp b/test/detail_misc_test.cpp
index 2fc38dfb..abebe783 100644
--- a/test/detail_misc_test.cpp
+++ b/test/detail_misc_test.cpp
@@ -7,7 +7,6 @@
 #include <boost/core/lightweight_test.hpp>
 #include <boost/core/lightweight_test_trait.hpp>
 #include <boost/histogram/accumulators/weighted_sum.hpp>
-#include <boost/histogram/detail/cat.hpp>
 #include <boost/histogram/detail/common_type.hpp>
 #include <boost/histogram/detail/counting_streambuf.hpp>
 #include <boost/histogram/detail/non_member_container_access.hpp>
@@ -23,9 +22,6 @@ using namespace boost::histogram::literals;
 namespace dtl = boost::histogram::detail;
 
 int main() {
-  // cat
-  { BOOST_TEST_EQ(dtl::cat("foo", 1, "bar"), "foo1bar"); }
-
   // literals
   {
     BOOST_TEST_TRAIT_SAME(std::integral_constant<unsigned, 0>, decltype(0_c));
diff --git a/test/utility_str.hpp b/test/utility_str.hpp
new file mode 100644
index 00000000..a7f67275
--- /dev/null
+++ b/test/utility_str.hpp
@@ -0,0 +1,20 @@
+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_HISTOGRAM_TEST_UTILITY_STR_HPP
+#define BOOST_HISTOGRAM_TEST_UTILITY_STR_HPP
+
+#include <sstream>
+#include <string>
+
+template <class T>
+std::string str(const T& t) {
+  std::ostringstream os;
+  os << t;
+  return os.str();
+}
+
+#endif