Separate argument parsing and formatting

fmt/format.h

@@ -3268,61 +3268,16 @@ struct precision_handler {
     return 0;
   }
 };
-}  // namespace internal
 
-template <typename Char>
-inline typename basic_context<Char>::format_arg
-  basic_context<Char>::get_arg(
-    basic_string_view<Char> name, const char *&error) {
-  if (this->check_no_auto_index(error)) {
-    map_.init(this->args());
-    if (const format_arg *arg = map_.find(name))
-      return *arg;
-    error = "argument not found";
-  }
-  return format_arg();
-}
 
-template <typename Char>
-inline typename basic_context<Char>::format_arg
-    basic_context<Char>::parse_arg_id() {
-  format_arg arg;
-  auto &it = this->pos();
-  if (!internal::is_name_start(*it)) {
-    const char *error = 0;
-    arg = *it < '0' || *it > '9' ?
-      this->next_arg(error) :
-      get_arg(internal::parse_nonnegative_int(it), error);
-    if (error) {
-      FMT_THROW(format_error(
-                  *it != '}' && *it != ':' ? "invalid format string" : error));
-    }
-    return arg;
-  }
-  auto start = it;
-  Char c;
-  do {
-    c = *++it;
-  } while (internal::is_name_start(c) || ('0' <= c && c <= '9'));
-  const char *error = 0;
-  arg = get_arg(basic_string_view<Char>(
-                  internal::pointer_from(start), it - start), error);
-  if (error)
-    FMT_THROW(format_error(error));
-  return arg;
-}
-
-// Formats a single argument.
-template <typename ArgFormatter, typename Char, typename Context>
-void do_format_arg(basic_buffer<Char> &buffer, const basic_arg<Context>& arg,
-                   Context &ctx) {
-  auto &it = ctx.pos();
+// Parses standard format specifiers.
+template <typename Context>
+basic_format_specs<typename Context::char_type>
+    parse_format_specs(const basic_arg<Context>& arg, Context &ctx) {
+  typedef typename Context::char_type Char;
   basic_format_specs<Char> spec;
-  if (*it == ':') {
-    if (visit(internal::custom_formatter<Char, Context>(buffer, ctx), arg))
-      return;
-    ++it;
   // Parse fill and alignment.
+  auto &it = ctx.pos();
   if (Char c = *it) {
     auto p = it + 1;
     spec.align_ = ALIGN_DEFAULT;
@@ -3429,6 +3384,20 @@ void do_format_arg(basic_buffer<Char> &buffer, const basic_arg<Context>& arg,
   // Parse type.
   if (*it != '}' && *it)
     spec.type_ = static_cast<char>(*it++);
+  return spec;
+}
+
+// Formats a single argument.
+template <typename ArgFormatter, typename Char, typename Context>
+void do_format_arg(basic_buffer<Char> &buffer, const basic_arg<Context>& arg,
+                   Context &ctx) {
+  auto &it = ctx.pos();
+  basic_format_specs<Char> spec;
+  if (*it == ':') {
+    if (visit(internal::custom_formatter<Char, Context>(buffer, ctx), arg))
+      return;
+    ++it;
+    spec = internal::parse_format_specs(arg, ctx);
   }
 
   if (*it != '}')
@@ -3437,6 +3406,49 @@ void do_format_arg(basic_buffer<Char> &buffer, const basic_arg<Context>& arg,
   // Format argument.
   visit(ArgFormatter(buffer, ctx, spec), arg);
 }
+}  // namespace internal
+
+template <typename Char>
+inline typename basic_context<Char>::format_arg
+  basic_context<Char>::get_arg(
+    basic_string_view<Char> name, const char *&error) {
+  if (this->check_no_auto_index(error)) {
+    map_.init(this->args());
+    if (const format_arg *arg = map_.find(name))
+      return *arg;
+    error = "argument not found";
+  }
+  return format_arg();
+}
+
+template <typename Char>
+inline typename basic_context<Char>::format_arg
+    basic_context<Char>::parse_arg_id() {
+  format_arg arg;
+  auto &it = this->pos();
+  if (!internal::is_name_start(*it)) {
+    const char *error = 0;
+    arg = *it < '0' || *it > '9' ?
+      this->next_arg(error) :
+      get_arg(internal::parse_nonnegative_int(it), error);
+    if (error) {
+      FMT_THROW(format_error(
+                  *it != '}' && *it != ':' ? "invalid format string" : error));
+    }
+    return arg;
+  }
+  auto start = it;
+  Char c;
+  do {
+    c = *++it;
+  } while (internal::is_name_start(c) || ('0' <= c && c <= '9'));
+  const char *error = 0;
+  arg = get_arg(basic_string_view<Char>(
+                  internal::pointer_from(start), it - start), error);
+  if (error)
+    FMT_THROW(format_error(error));
+  return arg;
+}
 
 /** Formats arguments and writes the output to the buffer. */
 template <typename ArgFormatter, typename Char, typename Context>
@@ -3457,7 +3469,7 @@ void vformat_to(basic_buffer<Char> &buffer, basic_string_view<Char> format_str,
     if (c == '}')
       FMT_THROW(format_error("unmatched '}' in format string"));
     buffer.append(pointer_from(start), pointer_from(it) - 1);
-    do_format_arg<ArgFormatter>(buffer, ctx.parse_arg_id(), ctx);
+    internal::do_format_arg<ArgFormatter>(buffer, ctx.parse_arg_id(), ctx);
     if (*it != '}')
       FMT_THROW(format_error(fmt::format("unknown format specifier")));
     start = ++it;

fmt/ostream.h

@@ -86,7 +86,7 @@ void format_value(basic_buffer<Char> &buf, const T &value,
   basic_memory_buffer<Char> buffer;
   internal::format_value(buffer, value);
   basic_string_view<Char> str(buffer.data(), buffer.size());
-  do_format_arg< arg_formatter<Char> >(
+  internal::do_format_arg< arg_formatter<Char> >(
         buf, internal::make_arg< basic_context<Char> >(str), ctx);
 }