Make it easier to define iterator ranges for APIs like getFoo(index).

We'll use this in AbstractionPattern.

Author: rjmccall

include/swift/Basic/IndexedViewRange.h

@@ -0,0 +1,100 @@
+//===- IndexedViewRange.h - Iterators for indexed projections ---*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines IndexedViewRange, a template class which makes it
+//  easy to define a range for a "collection" that is normally just vended
+//  with an indexed accessor.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_BASIC_INDEXEDVIEWRANGE_H
+#define SWIFT_BASIC_INDEXEDVIEWRANGE_H
+
+#include <iterator>
+#include <memory>
+#include "llvm/ADT/iterator_range.h"
+
+namespace swift {
+
+/// An iterator over a range of values provided by an indexed accessor
+/// on a base type.
+template <class BaseType, class ProjectedType,
+          ProjectedType (&Project)(BaseType, size_t)>
+class IndexedViewIterator {
+public:
+  using value_type = ProjectedType;
+  using reference = ProjectedType;
+  using pointer = void;
+  using difference_type = ptrdiff_t;
+  using iterator_category = std::random_access_iterator_tag;
+private:
+  BaseType Base;
+  size_t Index;
+public:
+  IndexedViewIterator(BaseType base, size_t index)
+    : Base(base), Index(index) {}
+public:
+  ProjectedType operator*() const { return Project(Base, Index); }
+  ProjectedType operator->() const { return Project(Base, Index); }
+  IndexedViewIterator &operator++() { Index++; return *this; }
+  IndexedViewIterator operator++(int) { return iterator(Base, Index++); }
+  IndexedViewIterator &operator--() { Index--; return *this; }
+  IndexedViewIterator operator--(int) { return iterator(Base, Index--); }
+  bool operator==(IndexedViewIterator rhs) const { return Index == rhs.Index; }
+  bool operator!=(IndexedViewIterator rhs) const { return Index != rhs.Index; }
+
+  IndexedViewIterator &operator+=(difference_type i) {
+    Index += i;
+    return *this;
+  }
+  IndexedViewIterator operator+(difference_type i) const {
+    return IndexedViewIterator(Base, Index + i);
+  }
+  friend IndexedViewIterator operator+(difference_type i,
+                                       IndexedViewIterator rhs) {
+    return IndexedViewIterator(rhs.Base, rhs.Index + i);
+  }
+  IndexedViewIterator &operator-=(difference_type i) {
+    Index -= i;
+    return *this;
+  }
+  IndexedViewIterator operator-(difference_type i) const {
+    return IndexedViewIterator(Base, Index - i);
+  }
+  difference_type operator-(IndexedViewIterator rhs) const {
+    return Index - rhs.Index;
+  }
+  ProjectedType operator[](difference_type i) const {
+    return Project(Base, Index + i);
+  }
+  bool operator<(IndexedViewIterator rhs) const {
+    return Index < rhs.Index;
+  }
+  bool operator<=(IndexedViewIterator rhs) const {
+    return Index <= rhs.Index;
+  }
+  bool operator>(IndexedViewIterator rhs) const {
+    return Index > rhs.Index;
+  }
+  bool operator>=(IndexedViewIterator rhs) const {
+    return Index >= rhs.Index;
+  }
+};
+
+template <class BaseType, class ProjectedType,
+          ProjectedType (&Project)(BaseType, size_t)>
+using IndexedViewRange =
+  llvm::iterator_range<IndexedViewIterator<BaseType, ProjectedType, Project>>;
+
+} // end namespace swift
+
+#endif // SWIFT_BASIC_INDEXEDVIEWRANGE_H