Move userspace to a templated StrFormat.

lib/glacier/string/string_builder.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "glacier/container/vector.h"
+#include "glacier/string/string.h"
+#include "glacier/string/string_view.h"
+
+namespace glcr {
+
+class StringBuilder : public Vector<char> {
+ public:
+  StringBuilder() : Vector<char>() {}
+  StringBuilder(const StringBuilder&) = delete;
+  StringBuilder(StringBuilder&& str) : Vector<char>(Move(str)) {}
+
+  void PushBack(const StringView& str);
+  using Vector<char>::PushBack;
+
+  String ToString() const;
+
+  // Note that this could become invalidated
+  // at any time if more characters are pushed
+  // onto the builder.
+  operator StringView() const;
+};
+
+}  // namespace glcr