[ADT] Add a generic iterator utility for adapting iterators much like

Boost's iterator_adaptor, and a specific adaptor which iterates over
pointees when wrapped around an iterator over pointers.

This is the result of a long discussion on IRC with Duncan Smith, Dave
Blaikie, Richard Smith, and myself. Essentially, I could use some subset
of the iterator facade facilities often used from Boost, and everyone
seemed interested in having the functionality in a reasonably generic
form. I've tried to strike a balance between the pragmatism and the
established Boost design. The primary differences are:

1) Delegating to the standard iterator interface names rather than
   special names that then make up a second iterator-like API.
2) Using the name 'pointee_iterator' which seems more clear than
   'indirect_iterator'. The whole business of calling the '*p' operation
   'pointer indirection' in the standard is ... quite confusing. And
   'dereference' is no better of a term for moving from a pointer to
   a reference.

Hoping Duncan, and others continue to provide comments on this until
we've got a nice, minimal abstraction.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207069 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2014-04-24 03:31:23 +00:00
parent c118614379
commit beee61d3e6
3 changed files with 206 additions and 1 deletions

145
include/llvm/ADT/iterator.h Normal file
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@ -0,0 +1,145 @@
//===- iterator.h - Utilities for using and defining iterators --*- 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_ITERATOR_H
#define LLVM_ADT_ITERATOR_H
#include <iterator>
namespace llvm {
/// \brief CRTP base class for adapting an iterator to a different type.
///
/// This class can be used through CRTP to adapt one iterator into another.
/// Typically this is done through providing in the derived class a custom \c
/// operator* implementation. Other methods can be overridden as well.
///
/// FIXME: Factor out the iterator-facade-like aspects into a base class that
/// can be used for defining completely custom iterators.
template <typename DerivedT, typename WrappedIteratorT, typename T,
typename PointerT = T *, typename ReferenceT = T &,
// Don't provide these, they are mostly to act as aliases below.
typename WrappedTraitsT = std::iterator_traits<WrappedIteratorT>>
class iterator_adaptor_base
: public std::iterator<typename WrappedTraitsT::iterator_category, T,
typename WrappedTraitsT::difference_type, PointerT,
ReferenceT> {
protected:
WrappedIteratorT I;
iterator_adaptor_base() {}
template <
typename U,
typename = typename std::enable_if<
!std::is_same<typename std::remove_cv<
typename std::remove_reference<U>::type>::type,
DerivedT>::value>::type>
explicit iterator_adaptor_base(U &&u)
: I(std::forward<U &&>(u)) {}
public:
typedef typename iterator_adaptor_base::iterator::difference_type
difference_type;
DerivedT &operator+=(difference_type n) {
I += n;
return *static_cast<DerivedT *>(this);
}
DerivedT &operator-=(difference_type n) {
I -= n;
return *static_cast<DerivedT *>(this);
}
DerivedT operator+(difference_type n) const {
DerivedT tmp = *this;
tmp += n;
return tmp;
}
friend DerivedT operator+(difference_type n, const DerivedT &i) {
return i + n;
}
DerivedT operator-(difference_type n) const {
DerivedT tmp = *this;
tmp -= n;
return tmp;
}
difference_type operator-(const DerivedT &RHS) const { return I - RHS.I; }
DerivedT &operator++() {
++I;
return *static_cast<DerivedT *>(this);
}
DerivedT &operator--() {
--I;
return *static_cast<DerivedT *>(this);
}
DerivedT operator++(int) {
DerivedT tmp = *static_cast<DerivedT *>(this);
++*this;
return tmp;
}
DerivedT operator--(int) {
DerivedT tmp = *static_cast<DerivedT *>(this);
--*this;
return tmp;
}
bool operator==(const DerivedT &RHS) const { return I == RHS.I; }
bool operator!=(const DerivedT &RHS) const {
return !static_cast<const DerivedT *>(this)->operator==(RHS);
}
bool operator<(const DerivedT &RHS) const { return I < RHS.I; }
bool operator>(const DerivedT &RHS) const {
return !static_cast<const DerivedT *>(this)->operator<(RHS) &&
!static_cast<const DerivedT *>(this)->operator==(RHS);
}
bool operator<=(const DerivedT &RHS) const {
return !static_cast<const DerivedT *>(this)->operator>(RHS);
}
bool operator>=(const DerivedT &RHS) const {
return !static_cast<const DerivedT *>(this)->operator<(RHS);
}
ReferenceT operator*() const { return *I; }
PointerT operator->() const {
return static_cast<const DerivedT *>(this)->operator*();
}
ReferenceT operator[](difference_type n) const {
return *static_cast<const DerivedT *>(this)->operator+(n);
}
};
/// \brief An iterator type that allows iterating over the pointees via some
/// other iterator.
///
/// The typical usage of this is to expose a type that iterates over Ts, but
/// which is implemented with some iterator over T*s:
///
/// \code
/// typedef pointee_iterator<SmallVectorImpl<T *>::iterator> iterator;
/// \endcode
template <
typename WrappedIteratorT,
typename T = typename std::remove_pointer<
typename std::iterator_traits<WrappedIteratorT>::value_type>::type>
struct pointee_iterator
: iterator_adaptor_base<pointee_iterator<WrappedIteratorT>,
WrappedIteratorT, T> {
pointee_iterator() {}
template <typename U>
pointee_iterator(U &&u)
: pointee_iterator::iterator_adaptor_base(std::forward<U &&>(u)) {}
T &operator*() const { return **this->I; }
};
}
#endif

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@ -15,12 +15,13 @@ add_llvm_unittest(SupportTests
EndianTest.cpp
ErrorOrTest.cpp
FileOutputBufferTest.cpp
IteratorTest.cpp
LEB128Test.cpp
LineIteratorTest.cpp
LockFileManagerTest.cpp
MD5Test.cpp
ManagedStatic.cpp
MathExtrasTest.cpp
MD5Test.cpp
MemoryBufferTest.cpp
MemoryTest.cpp
Path.cpp

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@ -0,0 +1,59 @@
//===- IteratorTest.cpp - Unit tests for iterator utilities ---------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/iterator.h"
#include "llvm/ADT/SmallVector.h"
#include "gtest/gtest.h"
using namespace llvm;
namespace {
TEST(PointeeIteratorTest, Basic) {
int arr[4] = { 1, 2, 3, 4 };
SmallVector<int *, 4> V;
V.push_back(&arr[0]);
V.push_back(&arr[1]);
V.push_back(&arr[2]);
V.push_back(&arr[3]);
typedef pointee_iterator<SmallVectorImpl<int *>::const_iterator> test_iterator;
test_iterator Begin, End;
Begin = V.begin();
End = test_iterator(V.end());
test_iterator I = Begin;
for (int i = 0; i < 4; ++i) {
EXPECT_EQ(*V[i], *I);
EXPECT_EQ(I, Begin + i);
EXPECT_EQ(I, std::next(Begin, i));
test_iterator J = Begin;
J += i;
EXPECT_EQ(I, J);
EXPECT_EQ(*V[i], Begin[i]);
EXPECT_NE(I, End);
EXPECT_GT(End, I);
EXPECT_LT(I, End);
EXPECT_GE(I, Begin);
EXPECT_LE(Begin, I);
EXPECT_EQ(i, I - Begin);
EXPECT_EQ(i, std::distance(Begin, I));
EXPECT_EQ(Begin, I - i);
test_iterator K = I++;
EXPECT_EQ(K, std::prev(I));
}
EXPECT_EQ(End, I);
}
} // anonymous namespace