diff --git a/octa/format.hh b/octa/format.hh
index 410d179..09462a9 100644
--- a/octa/format.hh
+++ b/octa/format.hh
@@ -17,47 +17,107 @@
 namespace octa {
 
 namespace detail {
-    template<typename R>
-    static inline void write_val(R &writer, const char *val) {
-        while (*val) writer.put(*val++);
-    }
+    /* C string */
 
     template<typename R>
-    static inline void write_val(R &writer, const octa::String &val) {
+    static inline octa::Size write_val(R &writer, const char *val) {
+        octa::Size n = 0;
+        while (*val) {
+            writer.put(*val++);
+            ++n;
+        }
+        return n;
+    }
+
+    /* OctaSTD string */
+
+    template<typename R>
+    static inline octa::Size write_val(R &writer, const octa::String &val) {
         for (octa::Size i = 0; i < val.size(); ++i) writer.put(val[i]);
+        return val.size();
+    }
+
+    /* A character */
+
+    template<typename R>
+    static inline octa::Size write_val(R &writer, char val) {
+        writer.put(val);
+        return 1;
+    }
+
+    /* Integer helpers */
+
+    template<typename R>
+    static inline octa::Size write_u(R &writer, octa::Uintmax val) {
+        char buf[20];
+        octa::Size n = 0;
+        for (; val; val /= 10) buf[n++] = '0' + val % 10;
+        for (int i = int(n - 1); i >= 0; --i) {
+            writer.put(buf[i]);
+        }
+        return n;
     }
 
     template<typename R>
-    static inline void write_val(R &writer, char val) {
-        writer.put(val);
+    static inline octa::Size write_i(R &writer, octa::Intmax val) {
+        octa::Uintmax uv;
+        int neg = 0;
+        if (val < 0) {
+            uv = -val;
+            writer.put('-');
+            neg = 1;
+        } else uv = val;
+        return octa::detail::write_u(writer, uv) + neg;
     }
 
+    template<typename R, typename T, bool = octa::IsIntegral<T>::value,
+                                     bool = octa::IsSigned<T>::value>
+    struct WriteIntVal {
+        static inline octa::Size write(R &writer, const T &val) {
+            return octa::detail::write_val(writer, octa::to_string(val));
+        }
+    };
+
+    template<typename R, typename T> struct WriteIntVal<R, T, true, true> {
+        static inline octa::Size write(R &writer, T val) {
+            return octa::detail::write_i(writer, val);
+        }
+    };
+
+    template<typename R, typename T> struct WriteIntVal<R, T, true, false> {
+        static inline octa::Size write(R &writer, T val) {
+            return octa::detail::write_u(writer, val);
+        }
+    };
+
+    /* Integers or generic value */
+
     template<typename R, typename T>
-    static inline void write_val(R &writer, const T &val) {
-        write_val(writer, octa::to_string(val));
+    static inline octa::Size write_val(R &writer, const T &val) {
+        return octa::detail::WriteIntVal<R, T>::write(writer, val);
     }
 
+    /* Writer entry point */
+
     template<typename R, typename T, typename ...A>
-    static inline void write_idx(R &writer, octa::Size idx, const T &v) {
+    static inline octa::Size write_idx(R &writer, octa::Size idx, const T &v) {
         if (idx) assert(false && "not enough format args");
-        write_val(writer, v);
+        return octa::detail::write_val(writer, v);
     }
 
     template<typename R, typename T, typename ...A>
-    static inline void write_idx(R &writer, octa::Size idx, const T &v,
-                                 A &&...args) {
-        if (idx) {
-            write_idx(writer, idx - 1, octa::forward<A>(args)...);
-            return;
-        }
-        write_val(writer, v);
+    static inline octa::Size write_idx(R &writer, octa::Size idx, const T &v,
+                                       const A &...args) {
+        if (idx)
+            return octa::detail::write_idx(writer, idx - 1, args...);
+        return octa::detail::write_val(writer, v);
     }
 } /* namespace detail */
 
 template<typename R, typename ...A>
-static inline octa::Size formatted_write(R writer, const char *fmt,
-                                         A &&...args) {
-    octa::Size argidx = 0, retn = 0;
+static inline octa::Size formatted_write(R writer, octa::Size &fmtn,
+                                         const char *fmt, const A &...args) {
+    octa::Size argidx = 0, written = 0, retn = 0;
     while (*fmt) {
         if (*fmt == '{') {
             octa::Size needidx = argidx;
@@ -70,18 +130,34 @@ static inline octa::Size formatted_write(R writer, const char *fmt,
             } else ++argidx;
             ++fmt;
             retn = octa::max(needidx, retn);
-            octa::detail::write_idx(writer, needidx,
-                octa::forward<A>(args)...);
+            written += octa::detail::write_idx(writer, needidx,
+                args...);
             continue;
         }
         writer.put(*fmt++);
+        ++written;
     }
-    return retn + 1;
+    fmtn = retn + 1;
+    return written;
 }
 
 template<typename R, typename ...A>
-octa::Size formatted_write(R writer, const octa::String &fmt, A &&...args) {
-    return formatted_write(writer, fmt.data(), octa::forward<A>(args)...);
+octa::Size formatted_write(R writer, octa::Size &fmtn, const octa::String &fmt,
+                           const A &...args) {
+    return formatted_write(writer, fmtn, fmt.data(), args...);
+}
+
+template<typename R, typename ...A>
+octa::Size formatted_write(R writer, const char *fmt, const A &...args) {
+    octa::Size fmtn = 0;
+    return formatted_write(writer, fmtn, fmt, args...);
+}
+
+template<typename R, typename ...A>
+octa::Size formatted_write(R writer, const octa::String &fmt,
+                           const A &...args) {
+    octa::Size fmtn = 0;
+    return formatted_write(writer, fmtn, fmt.data(), args...);
 }
 
 } /* namespace octa */
diff --git a/octa/io.hh b/octa/io.hh
index 7d93f8a..2ea5d3f 100644
--- a/octa/io.hh
+++ b/octa/io.hh
@@ -152,49 +152,36 @@ static inline void writeln(const T &v, const A &...args) {
     putc('\n', ::stdout);
 }
 
-namespace detail {
-    struct FormatOutRange: octa::OutputRange<char> {
-        FormatOutRange(): needed(0) {}
-        octa::Size needed;
-        char buf[512];
-        void put(char v) {
-            if (needed < sizeof(buf))
-                buf[needed] = v;
-            ++needed;
-        }
-    };
-}
-
 template<typename ...A>
-static inline void writef(const char *fmt, A &&...args) {
-    octa::detail::FormatOutRange writer1;
-    octa::formatted_write<octa::detail::FormatOutRange &>(writer1, fmt,
-        octa::forward<A>(args)...);
-    if (writer1.needed < sizeof(writer1.buf)) {
-        fwrite(writer1.buf, 1, writer1.needed, ::stdout);
+static inline void writef(const char *fmt, const A &...args) {
+    char buf[512];
+    octa::Size need = octa::formatted_write(octa::detail::FormatOutRange<
+        sizeof(buf)>(buf), fmt, args...);
+    if (need < sizeof(buf)) {
+        fwrite(buf, 1, need, ::stdout);
         return;
     }
     octa::String s;
-    s.reserve(writer1.needed);
-    s[writer1.needed] = '\0';
-    octa::formatted_write(s.iter(), fmt, octa::forward<A>(args)...);
-    fwrite(s.data(), 1, writer1.needed, ::stdout);
+    s.reserve(need);
+    s[need] = '\0';
+    octa::formatted_write(s.iter(), fmt, args...);
+    fwrite(s.data(), 1, need, ::stdout);
 }
 
 template<typename ...A>
-static inline void writef(const octa::String &fmt, A &&...args) {
-    writef(fmt.data(), octa::forward<A>(args)...);
+static inline void writef(const octa::String &fmt, const A &...args) {
+    writef(fmt.data(), args...);
 }
 
 template<typename ...A>
-static inline void writefln(const char *fmt, A &&...args) {
-    writef(fmt, octa::forward<A>(args)...);
+static inline void writefln(const char *fmt, const A &...args) {
+    writef(fmt, args...);
     putc('\n', ::stdout);
 }
 
 template<typename ...A>
-static inline void writefln(const octa::String &fmt, A &&...args) {
-    writef(fmt, octa::forward<A>(args)...);
+static inline void writefln(const octa::String &fmt, const A &...args) {
+    writef(fmt, args...);
     putc('\n', ::stdout);
 }
 
diff --git a/octa/stream.hh b/octa/stream.hh
index 3d9ede5..9bb286b 100644
--- a/octa/stream.hh
+++ b/octa/stream.hh
@@ -13,6 +13,7 @@
 #include "octa/type_traits.hh"
 #include "octa/string.hh"
 #include "octa/utility.hh"
+#include "octa/format.hh"
 
 namespace octa {
 
@@ -28,6 +29,17 @@ enum class StreamSeek {
 template<typename T = char, bool = octa::IsPod<T>::value>
 struct StreamRange;
 
+namespace detail {
+    template<octa::Size N>
+    struct FormatOutRange: octa::OutputRange<char> {
+        FormatOutRange(char *buf): buf(buf), idx(0) {}
+        FormatOutRange(const FormatOutRange &r): buf(r.buf), idx(r.idx) {}
+        char *buf;
+        octa::Size idx;
+        void put(char v) { if (idx < N) buf[idx++] = v; }
+    };
+}
+
 struct Stream {
     using Offset = StreamOffset;
 
@@ -84,20 +96,49 @@ struct Stream {
     }
 
     virtual bool writeln(const octa::String &s) {
-        return write(s) && write('\n');
+        return write(s) && putchar('\n');
     }
 
     virtual bool writeln(const char *s) {
-        return write(s) && write('\n');
+        return write(s) && putchar('\n');
     }
 
     template<typename T> bool writeln(const T &v) {
-        return writeln(octa::to_string(v));
+        return write(v) && putchar('\n');
     }
 
     template<typename T, typename ...A>
     bool writeln(const T &v, const A &...args) {
-        return write(v) && write(args...) && write('\n');
+        return write(v) && write(args...) && putchar('\n');
+    }
+
+    template<typename ...A>
+    bool writef(const char *fmt, const A &...args) {
+        char buf[512];
+        octa::Size need = octa::formatted_write(octa::detail::FormatOutRange<
+            sizeof(buf)>(buf), fmt, args...);
+        if (need < sizeof(buf))
+            return write_bytes(buf, need) == need;
+        octa::String s;
+        s.reserve(need);
+        s[need] = '\0';
+        octa::formatted_write(s.iter(), fmt, args...);
+        return write_bytes(s.data(), need) == need;
+    }
+
+    template<typename ...A>
+    bool writef(const octa::String &fmt, const A &...args) {
+        return writef(fmt.data(), args...);
+    }
+
+    template<typename ...A>
+    bool writefln(const char *fmt, const A &...args) {
+        return writef(fmt, args...) && putchar('\n');
+    }
+
+    template<typename ...A>
+    bool writefln(const octa::String &fmt, const A &...args) {
+        return writefln(fmt.data(), args...);
     }
 
     template<typename T = char>
diff --git a/octa/string.hh b/octa/string.hh
index 2eedd78..c8f0ffa 100644
--- a/octa/string.hh
+++ b/octa/string.hh
@@ -517,25 +517,25 @@ template<typename T> struct ToString<T *> {
 };
 
 template<> struct ToString<String> {
-    using Argument = const String &;
+    using Argument = String;
     using Result = String;
-    String operator()(Argument s) {
+    String operator()(const Argument &s) {
         return s;
     }
 };
 
 template<> struct ToString<StringRange> {
-    using Argument = const StringRange &;
+    using Argument = StringRange;
     using Result = String;
-    String operator()(Argument s) {
+    String operator()(const Argument &s) {
         return String(s);
     }
 };
 
 template<typename T, typename U> struct ToString<octa::Pair<T, U>> {
-    using Argument = const octa::Pair<T, U> &;
+    using Argument = octa::Pair<T, U>;
     using Result = String;
-    String operator()(Argument v) {
+    String operator()(const Argument &v) {
         String ret("{");
         ret += ToString<octa::RemoveCv<octa::RemoveReference<T>>>()
             (v.first);
diff --git a/octa/type_traits.hh b/octa/type_traits.hh
index 4180803..12f0b11 100644
--- a/octa/type_traits.hh
+++ b/octa/type_traits.hh
@@ -303,13 +303,29 @@ struct IsPolymorphic: IntegralConstant<bool, __is_polymorphic(T)> {};
 
 /* is signed */
 
+namespace detail {
+    template<typename T>
+    struct IsSignedBase: IntegralConstant<bool, T(-1) < T(0)> {};
+}
+
+template<typename T, bool = octa::IsArithmetic<T>::value>
+struct IsSigned: False {};
+
 template<typename T>
-struct IsSigned: IntegralConstant<bool, T(-1) < T(0)> {};
+struct IsSigned<T, true>: octa::detail::IsSignedBase<T> {};
 
 /* is unsigned */
 
+namespace detail {
+    template<typename T>
+    struct IsUnsignedBase: IntegralConstant<bool, T(0) < T(-1)> {};
+}
+
+template<typename T, bool = octa::IsArithmetic<T>::value>
+struct IsUnsigned: False {};
+
 template<typename T>
-struct IsUnsigned: IntegralConstant<bool, T(0) < T(-1)> {};
+struct IsUnsigned<T, true>: octa::detail::IsUnsignedBase<T> {};
 
 /* is standard layout */