Add support for using C++17 string_view or a fallback

Define a `cm::string_view` type implemented via C++17 `std::string_view`
when available.  Provide a fallback implementation for C++11 and C++14
compilers.

The fallback implementation was written by reading documentation of the
standard spec.  We have no dedicated tests for it, but it will be
covered by tests of its clients later.

1 files changed, 301 insertions, 0 deletions

diff --git a/Source/cm_string_view.cxx b/Source/cm_string_view.cxx
new file mode 100644
index 0000000000..61fa80e82a
--- /dev/null
+++ b/Source/cm_string_view.cxx
@@ -0,0 +1,301 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+#include "cm_string_view.hxx"
+
+#ifndef CMake_HAVE_CXX_STRING_VIEW
+
+#  include "cm_kwiml.h"
+
+#  include <algorithm>
+#  include <ostream>
+#  include <stdexcept>
+
+namespace cm {
+
+string_view::const_reference string_view::at(size_type pos) const
+{
+  if (pos >= size_) {
+    throw std::out_of_range("Index out of range in string_view::at");
+  }
+  return data_[pos];
+}
+
+string_view::size_type string_view::copy(char* dest, size_type count,
+                                         size_type pos) const
+{
+  if (pos > size_) {
+    throw std::out_of_range("Index out of range in string_view::copy");
+  }
+  size_type const rcount = std::min(count, size_ - pos);
+  traits_type::copy(dest, data_ + pos, rcount);
+  return rcount;
+}
+
+string_view string_view::substr(size_type pos, size_type count) const
+{
+  if (pos > size_) {
+    throw std::out_of_range("Index out of range in string_view::substr");
+  }
+  size_type const rcount = std::min(count, size_ - pos);
+  return string_view(data_ + pos, rcount);
+}
+
+int string_view::compare(string_view v) const noexcept
+{
+  size_type const rlen = std::min(size_, v.size_);
+  int c = traits_type::compare(data_, v.data_, rlen);
+  if (c == 0) {
+    if (size_ < v.size_) {
+      c = -1;
+    } else if (size_ > v.size_) {
+      c = 1;
+    }
+  }
+  return c;
+}
+
+int string_view::compare(size_type pos1, size_type count1, string_view v) const
+{
+  return substr(pos1, count1).compare(v);
+}
+
+int string_view::compare(size_type pos1, size_type count1, string_view v,
+                         size_type pos2, size_type count2) const
+{
+  return substr(pos1, count1).compare(v.substr(pos2, count2));
+}
+
+int string_view::compare(const char* s) const
+{
+  return compare(string_view(s));
+}
+
+int string_view::compare(size_type pos1, size_type count1, const char* s) const
+{
+  return substr(pos1, count1).compare(string_view(s));
+}
+
+int string_view::compare(size_type pos1, size_type count1, const char* s,
+                         size_type count2) const
+{
+  return substr(pos1, count1).compare(string_view(s, count2));
+}
+
+string_view::size_type string_view::find(string_view v, size_type pos) const
+  noexcept
+{
+  for (; pos + v.size_ <= size_; ++pos) {
+    if (std::char_traits<char>::compare(data_ + pos, v.data_, v.size_) == 0) {
+      return pos;
+    }
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find(char c, size_type pos) const noexcept
+{
+  return find(string_view(&c, 1), pos);
+}
+
+string_view::size_type string_view::find(const char* s, size_type pos,
+                                         size_type count) const
+{
+  return find(string_view(s, count), pos);
+}
+
+string_view::size_type string_view::find(const char* s, size_type pos) const
+{
+  return find(string_view(s), pos);
+}
+
+string_view::size_type string_view::rfind(string_view v, size_type pos) const
+  noexcept
+{
+  if (size_ >= v.size_) {
+    for (pos = std::min(pos, size_ - v.size_) + 1; pos > 0;) {
+      --pos;
+      if (std::char_traits<char>::compare(data_ + pos, v.data_, v.size_) ==
+          0) {
+        return pos;
+      }
+    }
+  }
+  return npos;
+}
+
+string_view::size_type string_view::rfind(char c, size_type pos) const noexcept
+{
+  return rfind(string_view(&c, 1), pos);
+}
+
+string_view::size_type string_view::rfind(const char* s, size_type pos,
+                                          size_type count) const
+{
+  return rfind(string_view(s, count), pos);
+}
+
+string_view::size_type string_view::rfind(const char* s, size_type pos) const
+{
+  return rfind(string_view(s), pos);
+}
+
+string_view::size_type string_view::find_first_of(string_view v,
+                                                  size_type pos) const noexcept
+{
+  for (; pos < size_; ++pos) {
+    if (traits_type::find(v.data_, v.size_, data_[pos])) {
+      return pos;
+    }
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_first_of(char c, size_type pos) const
+  noexcept
+{
+  return find_first_of(string_view(&c, 1), pos);
+}
+
+string_view::size_type string_view::find_first_of(const char* s, size_type pos,
+                                                  size_type count) const
+{
+  return find_first_of(string_view(s, count), pos);
+}
+
+string_view::size_type string_view::find_first_of(const char* s,
+                                                  size_type pos) const
+{
+  return find_first_of(string_view(s), pos);
+}
+
+string_view::size_type string_view::find_last_of(string_view v,
+                                                 size_type pos) const noexcept
+{
+  if (size_ > 0) {
+    for (pos = std::min(pos, size_ - 1) + 1; pos > 0;) {
+      --pos;
+      if (traits_type::find(v.data_, v.size_, data_[pos])) {
+        return pos;
+      }
+    }
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_last_of(char c, size_type pos) const
+  noexcept
+{
+  return find_last_of(string_view(&c, 1), pos);
+}
+
+string_view::size_type string_view::find_last_of(const char* s, size_type pos,
+                                                 size_type count) const
+{
+  return find_last_of(string_view(s, count), pos);
+}
+
+string_view::size_type string_view::find_last_of(const char* s,
+                                                 size_type pos) const
+{
+  return find_last_of(string_view(s), pos);
+}
+
+string_view::size_type string_view::find_first_not_of(string_view v,
+                                                      size_type pos) const
+  noexcept
+{
+  for (; pos < size_; ++pos) {
+    if (!traits_type::find(v.data_, v.size_, data_[pos])) {
+      return pos;
+    }
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_first_not_of(char c,
+                                                      size_type pos) const
+  noexcept
+{
+  return find_first_not_of(string_view(&c, 1), pos);
+}
+
+string_view::size_type string_view::find_first_not_of(const char* s,
+                                                      size_type pos,
+                                                      size_type count) const
+{
+  return find_first_not_of(string_view(s, count), pos);
+}
+
+string_view::size_type string_view::find_first_not_of(const char* s,
+                                                      size_type pos) const
+{
+  return find_first_not_of(string_view(s), pos);
+}
+
+string_view::size_type string_view::find_last_not_of(string_view v,
+                                                     size_type pos) const
+  noexcept
+{
+  if (size_ > 0) {
+    for (pos = std::min(pos, size_ - 1) + 1; pos > 0;) {
+      --pos;
+      if (!traits_type::find(v.data_, v.size_, data_[pos])) {
+        return pos;
+      }
+    }
+  }
+  return npos;
+}
+
+string_view::size_type string_view::find_last_not_of(char c,
+                                                     size_type pos) const
+  noexcept
+{
+  return find_last_not_of(string_view(&c, 1), pos);
+}
+
+string_view::size_type string_view::find_last_not_of(const char* s,
+                                                     size_type pos,
+                                                     size_type count) const
+{
+  return find_last_not_of(string_view(s, count), pos);
+}
+
+string_view::size_type string_view::find_last_not_of(const char* s,
+                                                     size_type pos) const
+{
+  return find_last_not_of(string_view(s), pos);
+}
+
+std::ostream& operator<<(std::ostream& o, string_view v)
+{
+  return o.write(v.data(), v.size());
+}
+
+std::string& operator+=(std::string& s, string_view v)
+{
+  s.append(v.data(), v.size());
+  return s;
+}
+}
+
+std::hash<cm::string_view>::result_type std::hash<cm::string_view>::operator()(
+  argument_type const& s) const noexcept
+{
+  // FNV-1a hash.
+  static KWIML_INT_uint64_t const fnv_offset_basis = 0xcbf29ce484222325;
+  static KWIML_INT_uint64_t const fnv_prime = 0x100000001b3;
+  KWIML_INT_uint64_t h = fnv_offset_basis;
+  for (char const& c : s) {
+    h = h ^ KWIML_INT_uint64_t(KWIML_INT_uint8_t(c));
+    h = h * fnv_prime;
+  }
+  return result_type(h);
+}
+#else
+// Avoid empty translation unit.
+void cm_string_view_cxx()
+{
+}
+#endif