add a new ArrayRef class. This is intended to replace the idiom we

use in many places where we pass a pointer and size to abstract APIs
that can take C arrays, std::vector, SmallVector, etc.  It is to arrays
what StringRef is to strings.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125486 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/ArrayRef.h

+//===--- ArrayRef.h - Array Reference Wrapper -------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_ARRAYREF_H
+#define LLVM_ADT_ARRAYREF_H
+
+#include "llvm/ADT/SmallVector.h"
+#include <vector>
+
+namespace llvm {
+  class APInt;
+  
+  /// ArrayRef - Represent a constant reference to an array (0 or more elements
+  /// consequtively in memory), i.e. a start pointer and a length.  It allows
+  /// various APIs to take consequtive elements easily and conveniently.
+  ///
+  /// This class does not own the underlying data, it is expected to be used in
+  /// situations where the data resides in some other buffer, whose lifetime
+  /// extends past that of the StringRef. For this reason, it is not in general
+  /// safe to store a ArrayRef.
+  ///
+  /// This is intended to be trivially copyable, so it should be passed by
+  /// value.
+  template<typename T>
+  class ArrayRef {
+  public:
+    typedef const T *iterator;
+    typedef const T *const_iterator;
+    typedef size_t size_type;
+    
+  private:
+    /// The start of the array, in an external buffer.
+    const T *Data;
+    
+    /// The number of elements.
+    size_t Length;
+    
+  public:
+    /// @name Constructors
+    /// @{
+    
+    /// Construct an empty ArrayRef.
+    /*implicit*/ ArrayRef() : Data(0), Length(0) {}
+    
+    /// Construct an ArrayRef from a single element.
+    /*implicit*/ ArrayRef(const T &OneElt)
+      : Data(&OneElt), Length(1) {}
+    
+    /// Construct an ArrayRef from a pointer and length.
+    /*implicit*/ ArrayRef(T *data, size_t length)
+      : Data(data), Length(length) {}
+    
+    /// Construct an ArrayRef from a SmallVector.
+    /*implicit*/ ArrayRef(const SmallVectorImpl<T> &Vec)
+      : Data(Vec.data()), Length(Vec.size()) {}
+
+    /// Construct an ArrayRef from a std::vector.
+    /*implicit*/ ArrayRef(const std::vector<T> &Vec)
+      : Data(Vec.empty() ? (T*)0 : &Vec[0]), Length(Vec.size()) {}
+    
+    // TODO: C arrays.
+    
+    /// @}
+    /// @name Simple Operations
+    /// @{
+
+    iterator begin() const { return Data; }
+    iterator end() const { return Data + Length; }
+    
+    /// empty - Check if the string is empty.
+    bool empty() const { return Length == 0; }
+    
+    /// size - Get the string size.
+    size_t size() const { return Length; }
+    
+    /// front - Get the first element.
+    const T &front() const {
+      assert(!empty());
+      return Data[0];
+    }
+    
+    /// back - Get the last character in the string.
+    const T &back() const {
+      assert(!empty());
+      return Data[Length-1];
+    }
+    
+    /// @}
+    /// @name Operator Overloads
+    /// @{
+    
+    char operator[](size_t Index) const {
+      assert(Index < Length && "Invalid index!");
+      return Data[Index];
+    }
+    
+    /// @}
+    /// @name Expensive Operations
+    /// @{
+    
+    std::vector<T> vec() const {
+      return std::vector<T>(Data, Data+Length);
+    }
+    
+    /// @}
+  };
+  
+  // ArrayRefs can be treated like a POD type.
+  template <typename T> struct isPodLike;
+  template <typename T> struct isPodLike<ArrayRef<T> > {
+    static const bool value = true;
+  };
+}
+
+#endif