[mathicgb] 378/393: Added missing Zip.hpp file.

[Doug Torrance]

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dtorrance-guest pushed a commit to branch upstream
in repository mathicgb.

commit cfef9d0387e043e959b01fadbe2e263644cae8dc
Author: Bjarke Hammersholt Roune <bjarkehr.code at gmail.com>
Date:   Fri Sep 20 12:37:43 2013 +0200

    Added missing Zip.hpp file.
---
 src/mathicgb/Zip.hpp | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)

diff --git a/src/mathicgb/Zip.hpp b/src/mathicgb/Zip.hpp
new file mode 100644
index 0000000..b51d650
--- /dev/null
+++ b/src/mathicgb/Zip.hpp
@@ -0,0 +1,91 @@
+// MathicGB copyright 2012 all rights reserved. MathicGB comes with ABSOLUTELY
+// NO WARRANTY and is licensed as GPL v2.0 or later - see LICENSE.txt.
+#ifndef MATHICGB_ZIP_GUARD
+#define MATHICGB_ZIP_GUARD
+
+#include "Range.hpp"
+
+MATHICGB_NAMESPACE_BEGIN
+
+/// Zip ties two iterators together into a single iterator. The point
+/// is to enable the zip() function defined further down in this header.
+template<class Iterator1, class Iterator2>
+class Zip {
+public:
+  typedef decltype(*std::declval<Iterator1>()) Value1;
+  typedef decltype(*std::declval<Iterator2>()) Value2;
+  typedef std::pair<Value1, Value2> value_type;
+
+  Zip() {}
+  Zip(Iterator1 it1, Iterator2 it2): mIt1(it1), mIt2(it2) {}
+
+  Zip& operator++() {
+    ++mIt1;
+    ++mIt2;
+    return *this;
+  }
+
+  value_type operator*() const {
+    // We cannot use std::make_pair here. If .first or .second is a reference,
+    // then std::make_pair will remove the reference and then the conversion
+    // to value_type will add the reference back in - but now the reference
+    // is not what was originally referenced, instead it is a reference to
+    // the temporary object returned by std::make_pair, which then promptly
+    // goes out of scope, leading to undefined behavior.
+    return value_type(*mIt1, *mIt2);
+  }
+
+  bool operator!=(const Zip& it) const {
+    MATHICGB_ASSERT((mIt1 != it.mIt1) == (mIt2 != it.mIt2));
+    return mIt1 != it.mIt1;
+  }
+
+  bool operator==(const Zip& it) const {
+    MATHICGB_ASSERT((mIt1 == it.mIt1) == (mIt2 == it.mIt2));
+    return mIt1 == it.mIt1;
+  }
+
+private:
+  Iterator1 mIt1;
+  Iterator2 mIt2;
+};
+
+/// Creates a Zip iterator out of it1 and it2. This is a convenience function
+/// that avoids the need to specify the iterator types explicitly.
+template<class Iterator1, class Iterator2>
+auto makeZip(
+  Iterator1&& it1,
+  Iterator2&& it2
+) -> Zip<Iterator1, Iterator2> {
+  return Zip<Iterator1, Iterator2>(
+    std::forward<Iterator1>(it1),
+    std::forward<Iterator2>(it2)
+  );
+}
+
+/// Zips two ranges into a single zipped range. Example:
+///
+///   std::vector<string> a = {"hello", "world"};
+///   std::vector<int> b = {4, 2};
+///   for (const auto& p : zip(a, b))
+///     std::cout << p.first << p.second << ' ';
+///
+/// The output will be "hello4 world2 ".
+template<class Range1, class Range2>
+auto zip(Range1&& range1, Range2&& range2) ->
+  decltype(
+    range(
+      makeZip(std::begin(range1), std::begin(range2)),
+      makeZip(std::end(range1), std::end(range2))
+    )
+  )
+{
+  return range(
+    makeZip(std::begin(range1), std::begin(range2)),
+    makeZip(std::end(range1), std::end(range2))
+  );
+}
+
+MATHICGB_NAMESPACE_END
+
+#endif

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