From: Tudor Bosman <tudorb@fb.com>
Date: Tue, 13 Nov 2012 03:46:41 +0000 (-0800)
Subject: add split operator
X-Git-Tag: v0.22.0~1144
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=ed4482475c02ded524019c347d271032d51553d4;p=folly.git

add split operator

Summary:
Also added eachAs (cast each value as a given type) and eachTo (use folly::to
on each value)

Test Plan: test added

Reviewed By: tjackson@fb.com

FB internal diff: D628868
---

diff --git a/folly/experimental/File-inl.h b/folly/experimental/File-inl.h
new file mode 100644
index 00000000..02240d6a
--- /dev/null
+++ b/folly/experimental/File-inl.h
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2012 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FOLLY_FILE_H_
+#error This file may only be included from folly/experimental/File.h
+#endif
+
+#include <algorithm>
+
+namespace folly {
+
+inline File::File(int fd, bool ownsFd) : fd_(fd), ownsFd_(ownsFd) { }
+
+inline File::~File() {
+  closeNoThrow();  // ignore error
+}
+
+inline void File::release() {
+  fd_ = -1;
+  ownsFd_ = false;
+}
+
+inline void File::swap(File& other) {
+  using std::swap;
+  swap(fd_, other.fd_);
+  swap(ownsFd_, other.ownsFd_);
+}
+
+inline File::File(File&& other) : fd_(other.fd_), ownsFd_(other.ownsFd_) {
+  other.release();
+}
+
+inline File& File::operator=(File&& other) {
+  File(std::move(other)).swap(*this);
+  return *this;
+}
+
+inline void swap(File& a, File& b) {
+  a.swap(b);
+}
+
+}  // namespace folly
+
diff --git a/folly/experimental/File.cpp b/folly/experimental/File.cpp
new file mode 100644
index 00000000..119ae924
--- /dev/null
+++ b/folly/experimental/File.cpp
@@ -0,0 +1,47 @@
+/*
+ * Copyright 2012 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "folly/experimental/File.h"
+
+#include <system_error>
+
+#include <glog/logging.h>
+
+namespace folly {
+
+File::File(const char* name, int flags, mode_t mode)
+  : fd_(::open(name, flags, mode)), ownsFd_(false) {
+  if (fd_ == -1) {
+    throw std::system_error(errno, std::system_category(), "open() failed");
+  }
+  ownsFd_ = true;
+}
+
+void File::close() {
+  if (!closeNoThrow()) {
+    throw std::system_error(errno, std::system_category(), "close() failed");
+  }
+}
+
+bool File::closeNoThrow() {
+  DCHECK(fd_ != -1);
+  int r = ownsFd_ ? ::close(fd_) : 0;
+  release();
+  return r == 0;
+}
+
+}  // namespace folly
+
diff --git a/folly/experimental/File.h b/folly/experimental/File.h
new file mode 100644
index 00000000..4fd69d6c
--- /dev/null
+++ b/folly/experimental/File.h
@@ -0,0 +1,90 @@
+/*
+ * Copyright 2012 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FOLLY_FILE_H_
+#define FOLLY_FILE_H_
+
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <fcntl.h>
+
+namespace folly {
+
+/**
+ * A File represents an open file.
+ */
+class File {
+ public:
+  /**
+   * Create a File object from an existing file descriptor.
+   * Takes ownership of the file descriptor if ownsFd is true.
+   */
+  /* implicit */ File(int fd, bool ownsFd=false);
+
+  /**
+   * Open and create a file object.  Throws on error.
+   */
+  /* implicit */ File(const char* name, int flags=O_RDONLY, mode_t mode=0644);
+
+  ~File();
+
+  /**
+   * Return the file descriptor, or -1 if the file was closed.
+   */
+  int fd() const { return fd_; }
+
+  /**
+   * If we own the file descriptor, close the file and throw on error.
+   * Otherwise, do nothing.
+   */
+  void close();
+
+  /**
+   * Closes the file (if owned).  Returns true on success, false (and sets
+   * errno) on error.
+   */
+  bool closeNoThrow();
+
+  /**
+   * Releases the file descriptor; no longer owned by this File.
+   */
+  void release();
+
+  /**
+   * Swap this File with another.
+   */
+  void swap(File& other);
+
+  // movable
+  File(File&&);
+  File& operator=(File&&);
+ private:
+  // not copyable
+  File(const File&) = delete;
+  File& operator=(const File&) = delete;
+
+  int fd_;
+  bool ownsFd_;
+};
+
+void swap(File& a, File& b);
+
+}  // namespace folly
+
+#include "folly/experimental/File-inl.h"
+
+#endif /* FOLLY_FILE_H_ */
+
diff --git a/folly/experimental/FileGen-inl.h b/folly/experimental/FileGen-inl.h
new file mode 100644
index 00000000..429cdd7b
--- /dev/null
+++ b/folly/experimental/FileGen-inl.h
@@ -0,0 +1,126 @@
+/*
+ * Copyright 2012 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FOLLY_FILEGEN_H_
+#error This file may only be included from folly/experimental/FileGen.h
+#endif
+
+#include <system_error>
+
+#include "folly/experimental/StringGen.h"
+
+namespace folly {
+namespace gen {
+namespace detail {
+
+class FileReader : public GenImpl<ByteRange, FileReader> {
+ public:
+  FileReader(File file, std::unique_ptr<IOBuf> buffer)
+    : file_(std::move(file)),
+      buffer_(std::move(buffer)) {
+    buffer_->clear();
+  }
+
+  template <class Body>
+  bool apply(Body&& body) const {
+    for (;;) {
+      ssize_t n = ::read(file_.fd(), buffer_->writableTail(),
+                         buffer_->capacity());
+      if (n == -1) {
+        throw std::system_error(errno, std::system_category(), "read failed");
+      }
+      if (n == 0) {
+        return true;
+      }
+      if (!body(ByteRange(buffer_->tail(), n))) {
+        return false;
+      }
+    }
+  }
+ private:
+  File file_;
+  std::unique_ptr<IOBuf> buffer_;
+};
+
+class FileWriter : public Operator<FileWriter> {
+ public:
+  FileWriter(File file, std::unique_ptr<IOBuf> buffer)
+    : file_(std::move(file)),
+      buffer_(std::move(buffer)) {
+    if (buffer_) {
+      buffer_->clear();
+    }
+  }
+
+  template <class Source, class Value>
+  void compose(const GenImpl<Value, Source>& source) const {
+    auto fn = [&](ByteRange v) {
+      if (!this->buffer_ || v.size() >= this->buffer_->capacity()) {
+        this->flushBuffer();
+        this->write(v);
+      } else {
+        if (v.size() > this->buffer_->tailroom()) {
+          this->flushBuffer();
+        }
+        memcpy(this->buffer_->writableTail(), v.data(), v.size());
+        this->buffer_->append(v.size());
+      }
+    };
+
+    // Iterate
+    source.foreach(std::move(fn));
+
+    flushBuffer();
+    file_.close();
+  }
+
+ private:
+  void write(ByteRange v) const {
+    ssize_t n;
+    while (!v.empty()) {
+      n = ::write(file_.fd(), v.data(), v.size());
+      if (n == -1) {
+        if (errno == EINTR) {
+          continue;
+        }
+        throw std::system_error(errno, std::system_category(),
+                                "write() failed");
+      }
+      v.advance(n);
+    }
+  }
+
+  void flushBuffer() const {
+    if (buffer_ && buffer_->length() != 0) {
+      write(ByteRange(buffer_->data(), buffer_->length()));
+      buffer_->clear();
+    }
+  }
+
+  mutable File file_;
+  std::unique_ptr<IOBuf> buffer_;
+};
+
+}  // namespace detail
+
+auto byLine(File file, char delim='\n') ->
+decltype(fromFile(std::move(file)) | eachAs<StringPiece>() | resplit(delim)) {
+  return fromFile(std::move(file)) | eachAs<StringPiece>() | resplit(delim);
+}
+
+}  // namespace gen
+}  // namespace folly
+
diff --git a/folly/experimental/FileGen.h b/folly/experimental/FileGen.h
new file mode 100644
index 00000000..ab5af127
--- /dev/null
+++ b/folly/experimental/FileGen.h
@@ -0,0 +1,74 @@
+/*
+ * Copyright 2012 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FOLLY_FILEGEN_H_
+#define FOLLY_FILEGEN_H_
+
+#include "folly/experimental/File.h"
+#include "folly/experimental/Gen.h"
+#include "folly/experimental/io/IOBuf.h"
+
+namespace folly {
+namespace gen {
+
+namespace detail {
+class FileReader;
+class FileWriter;
+}  // namespace detail
+
+/**
+ * Generator that reads from a file with a buffer of the given size.
+ * Reads must be buffered (the generator interface expects the generator
+ * to hold each value).
+ */
+template <class S = detail::FileReader>
+S fromFile(File file, size_t bufferSize=4096) {
+  return S(std::move(file), IOBuf::create(bufferSize));
+}
+
+/**
+ * Generator that reads from a file using a given buffer.
+ */
+template <class S = detail::FileReader>
+S fromFile(File file, std::unique_ptr<IOBuf> buffer) {
+  return S(std::move(file), std::move(buffer));
+}
+
+/**
+ * Sink that writes to a file with a buffer of the given size.
+ * If bufferSize is 0, writes will be unbuffered.
+ */
+template <class S = detail::FileWriter>
+S toFile(File file, size_t bufferSize=4096) {
+  return S(std::move(file), bufferSize ? nullptr : IOBuf::create(bufferSize));
+}
+
+/**
+ * Sink that writes to a file using a given buffer.
+ * If the buffer is nullptr, writes will be unbuffered.
+ */
+template <class S = detail::FileWriter>
+S toFile(File file, std::unique_ptr<IOBuf> buffer) {
+  return S(std::move(file), std::move(buffer));
+}
+
+}  // namespace gen
+}  // namespace folly
+
+#include "folly/experimental/FileGen-inl.h"
+
+#endif /* FOLLY_FILEGEN_H_ */
+
diff --git a/folly/experimental/Gen-inl.h b/folly/experimental/Gen-inl.h
index 5079ae22..95f0b76f 100644
--- a/folly/experimental/Gen-inl.h
+++ b/folly/experimental/Gen-inl.h
@@ -261,7 +261,7 @@ template<class Value,
          class Gen,
          class Op>
 auto operator|(const GenImpl<Value, Gen>& gen, const Operator<Op>& op) ->
-decltype(op.self().compose(gen)) {
+decltype(op.self().compose(gen.self())) {
   return op.self().compose(gen.self());
 }
 
@@ -291,7 +291,7 @@ template<class Container,
          class Value>
 class ReferencedSource :
     public GenImpl<Value, ReferencedSource<Container, Value>> {
-  Container* const container_;
+  Container* container_;
 public:
   explicit ReferencedSource(Container* container)
     : container_(container) {}
@@ -344,7 +344,7 @@ class CopiedSource :
   static_assert(
     !std::is_reference<Container>::value,
     "Can't copy into a reference");
-  const std::shared_ptr<const Container> copy_;
+  std::shared_ptr<const Container> copy_;
 public:
   typedef Container ContainerType;
 
@@ -451,8 +451,8 @@ public:
 template<class Value, class First, class Second>
 class Chain : public GenImpl<Value,
                              Chain<Value, First, Second>> {
-  const First first_;
-  const Second second_;
+  First first_;
+  Second second_;
 public:
   explicit Chain(First first, Second second)
       : first_(std::move(first))
@@ -477,7 +477,7 @@ public:
  **/
 template<class Value, class Source>
 class Yield : public GenImpl<Value, Yield<Value, Source>> {
-  const Source source_;
+  Source source_;
  public:
   explicit Yield(Source source)
     : source_(std::move(source)) {
@@ -520,7 +520,7 @@ class Yield : public GenImpl<Value, Yield<Value, Source>> {
  */
 template<class Predicate>
 class Map : public Operator<Map<Predicate>> {
-  const Predicate predicate_;
+  Predicate predicate_;
  public:
   explicit Map(const Predicate& predicate = Predicate())
     : predicate_(predicate)
@@ -533,8 +533,8 @@ class Map : public Operator<Map<Predicate>> {
                           >::type>
   class Generator :
       public GenImpl<Result, Generator<Value, Source, Result>> {
-    const Source source_;
-    const Predicate pred_;
+    Source source_;
+    Predicate pred_;
   public:
     explicit Generator(Source source, const Predicate& pred)
       : source_(std::move(source)), pred_(pred) {}
@@ -582,7 +582,7 @@ class Map : public Operator<Map<Predicate>> {
  */
 template<class Predicate>
 class Filter : public Operator<Filter<Predicate>> {
-  const Predicate predicate_;
+  Predicate predicate_;
  public:
   explicit Filter(const Predicate& predicate)
     : predicate_(predicate)
@@ -591,8 +591,8 @@ class Filter : public Operator<Filter<Predicate>> {
   template<class Value,
            class Source>
   class Generator : public GenImpl<Value, Generator<Value, Source>> {
-    const Source source_;
-    const Predicate pred_;
+    Source source_;
+    Predicate pred_;
   public:
     explicit Generator(Source source, const Predicate& pred)
       : source_(std::move(source)), pred_(pred) {}
@@ -643,7 +643,7 @@ class Filter : public Operator<Filter<Predicate>> {
  */
 template<class Predicate>
 class Until : public Operator<Until<Predicate>> {
-  const Predicate predicate_;
+  Predicate predicate_;
  public:
   explicit Until(const Predicate& predicate)
     : predicate_(predicate)
@@ -654,8 +654,8 @@ class Until : public Operator<Until<Predicate>> {
            class Result = typename std::result_of<Predicate(Value)>::type>
   class Generator :
       public GenImpl<Result, Generator<Value, Source, Result>> {
-    const Source source_;
-    const Predicate pred_;
+    Source source_;
+    Predicate pred_;
   public:
     explicit Generator(Source source, const Predicate& pred)
       : source_(std::move(source)), pred_(pred) {}
@@ -694,7 +694,7 @@ class Until : public Operator<Until<Predicate>> {
  *             | take(10);
  */
 class Take : public Operator<Take> {
-  const size_t count_;
+  size_t count_;
 public:
   explicit Take(size_t count)
     : count_(count) {}
@@ -703,8 +703,8 @@ public:
            class Source>
   class Generator :
       public GenImpl<Value, Generator<Value, Source>> {
-    const Source source_;
-    const size_t count_;
+    Source source_;
+    size_t count_;
   public:
     explicit Generator(Source source, size_t count)
       : source_(std::move(source)) , count_(count) {}
@@ -747,7 +747,7 @@ public:
  *             | take(10);
  */
 class Skip : public Operator<Skip> {
-  const size_t count_;
+  size_t count_;
 public:
   explicit Skip(size_t count)
     : count_(count) {}
@@ -756,8 +756,8 @@ public:
            class Source>
   class Generator :
       public GenImpl<Value, Generator<Value, Source>> {
-    const Source source_;
-    const size_t count_;
+    Source source_;
+    size_t count_;
   public:
     explicit Generator(Source source, size_t count)
       : source_(std::move(source)) , count_(count) {}
@@ -824,8 +824,8 @@ public:
  */
 template<class Selector, class Comparer>
 class Order : public Operator<Order<Selector, Comparer>> {
-  const Selector selector_;
-  const Comparer comparer_;
+  Selector selector_;
+  Comparer comparer_;
  public:
   Order(const Selector& selector = Selector(),
         const Comparer& comparer = Comparer())
@@ -838,9 +838,9 @@ class Order : public Operator<Order<Selector, Comparer>> {
   class Generator :
     public GenImpl<StorageType&&,
                    Generator<Value, Source, StorageType, Result>> {
-    const Source source_;
-    const Selector selector_;
-    const Comparer comparer_;
+    Source source_;
+    Selector selector_;
+    Comparer comparer_;
 
     typedef std::vector<StorageType> VectorType;
 
@@ -923,8 +923,8 @@ class Order : public Operator<Order<Selector, Comparer>> {
 template<class First,
          class Second>
 class Composed : public Operator<Composed<First, Second>> {
-  const First first_;
-  const Second second_;
+  First first_;
+  Second second_;
   public:
     Composed() {}
     Composed(First first, Second second)
@@ -971,8 +971,8 @@ class Composed : public Operator<Composed<First, Second>> {
 template<class Seed,
          class Fold>
 class FoldLeft : public Operator<FoldLeft<Seed, Fold>> {
-  const Seed seed_;
-  const Fold fold_;
+  Seed seed_;
+  Fold fold_;
  public:
   FoldLeft(const Seed& seed, const Fold& fold)
     : seed_(seed)
@@ -1052,7 +1052,7 @@ class Any : public Operator<Any> {
  */
 template<class Reducer>
 class Reduce : public Operator<Reduce<Reducer>> {
-  const Reducer reducer_;
+  Reducer reducer_;
  public:
   Reduce(const Reducer& reducer)
     : reducer_(reducer)
@@ -1175,7 +1175,7 @@ class Min : public Operator<Min<Selector, Comparer>> {
  */
 template<class Collection>
 class Append : public Operator<Append<Collection>> {
-  Collection* const collection_;
+  Collection* collection_;
  public:
   explicit Append(Collection* collection)
     : collection_(collection)
@@ -1271,7 +1271,7 @@ public:
            class InnerValue = typename std::decay<Inner>::type::ValueType>
   class Generator :
       public GenImpl<InnerValue, Generator<Inner, Source, InnerValue>> {
-    const Source source_;
+    Source source_;
   public:
     explicit Generator(Source source)
       : source_(std::move(source)) {}
@@ -1325,7 +1325,7 @@ public:
            class InnerValue = typename ValueTypeOfRange<Range>::RefType>
   class Generator
     : public GenImpl<InnerValue, Generator<Source, Range, InnerValue>> {
-    const Source source_;
+    Source source_;
    public:
     explicit Generator(Source source)
       : source_(std::move(source)) {}
@@ -1393,7 +1393,7 @@ class VirtualGen : public GenImpl<Value, VirtualGen<Value>> {
 
   template<class Wrapped>
   class WrapperImpl : public WrapperBase {
-    const Wrapped wrapped_;
+    Wrapped wrapped_;
    public:
     explicit WrapperImpl(Wrapped wrapped)
      : wrapped_(std::move(wrapped)) {
diff --git a/folly/experimental/Gen.h b/folly/experimental/Gen.h
index 9126d59b..457c6e5c 100644
--- a/folly/experimental/Gen.h
+++ b/folly/experimental/Gen.h
@@ -24,6 +24,7 @@
 
 #include "folly/Range.h"
 #include "folly/Optional.h"
+#include "folly/Conv.h"
 
 /**
  * Generator-based Sequence Comprehensions in C++, akin to C#'s LINQ
@@ -135,6 +136,24 @@ public:
   }
 };
 
+template <class Dest>
+class Cast {
+ public:
+  template <class Value>
+  Dest operator()(Value&& value) const {
+    return Dest(std::forward<Value>(value));
+  }
+};
+
+template <class Dest>
+class To {
+ public:
+  template <class Value>
+  Dest operator()(Value&& value) const {
+    return ::folly::to<Dest>(std::forward<Value>(value));
+  }
+};
+
 namespace detail {
 
 template<class Self>
@@ -343,6 +362,20 @@ Get get() {
   return Get();
 }
 
+// construct Dest from each value
+template <class Dest,
+          class Cast = detail::Map<Cast<Dest>>>
+Cast eachAs() {
+  return Cast();
+}
+
+// call folly::to on each value
+template <class Dest,
+          class To = detail::Map<To<Dest>>>
+To eachTo() {
+  return To();
+}
+
 /*
  * Sink Factories
  */
diff --git a/folly/experimental/StringGen-inl.h b/folly/experimental/StringGen-inl.h
new file mode 100644
index 00000000..3330e8b5
--- /dev/null
+++ b/folly/experimental/StringGen-inl.h
@@ -0,0 +1,130 @@
+/*
+ * Copyright 2012 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FOLLY_STRINGGEN_H_
+#error This file may only be included from folly/experimental/StringGen.h
+#endif
+
+#include "folly/experimental/io/IOBuf.h"
+
+namespace folly {
+namespace gen {
+namespace detail {
+
+bool splitPrefix(StringPiece& in, StringPiece& prefix, char delimiter) {
+  auto p = static_cast<const char*>(memchr(in.data(), delimiter, in.size()));
+  if (p) {
+    prefix.assign(in.data(), p);
+    in.assign(p + 1, in.end());
+    return true;
+  }
+  prefix.clear();
+  return false;
+}
+
+inline const char* ch(const unsigned char* p) {
+  return reinterpret_cast<const char*>(p);
+}
+
+class StringResplitter : public Operator<StringResplitter> {
+  char delimiter_;
+ public:
+  explicit StringResplitter(char delimiter) : delimiter_(delimiter) { }
+
+  template <class Source>
+  class Generator : public GenImpl<StringPiece, Generator<Source>> {
+    Source source_;
+    char delimiter_;
+    static constexpr size_t kDefaultLineSize = 256;
+   public:
+    Generator(Source source, char delimiter)
+      : source_(std::move(source)), delimiter_(delimiter) { }
+
+    template <class Body>
+    bool apply(Body&& body) const {
+      std::unique_ptr<IOBuf> buffer;
+
+      auto fn = [&](StringPiece in) -> bool {
+        StringPiece prefix;
+        bool found = splitPrefix(in, prefix, this->delimiter_);
+        if (found && buffer && buffer->length() != 0) {
+          // Append to end of buffer, return line
+          if (!prefix.empty()) {
+            buffer->reserve(0, prefix.size());
+            memcpy(buffer->writableTail(), prefix.data(), prefix.size());
+            buffer->append(prefix.size());
+          }
+          if (!body(StringPiece(ch(buffer->data()), buffer->length()))) {
+            return false;
+          }
+          buffer->clear();
+          found = splitPrefix(in, prefix, this->delimiter_);
+        }
+        // Buffer is empty, return lines directly from input (no buffer)
+        while (found) {
+          if (!body(prefix)) {
+            return false;
+          }
+          found = splitPrefix(in, prefix, this->delimiter_);
+        }
+        if (!in.empty()) {
+          // Incomplete line left, append to buffer
+          if (!buffer) {
+            // Arbitrarily assume that we have half a line and get enough
+            // room for twice that.
+            buffer = IOBuf::create(std::max(kDefaultLineSize, 2 * in.size()));
+          }
+          buffer->reserve(0, in.size());
+          memcpy(buffer->writableTail(), in.data(), in.size());
+          buffer->append(in.size());
+        }
+        return true;
+      };
+
+      // Iterate
+      if (!source_.apply(std::move(fn))) {
+        return false;
+      }
+
+      // Incomplete last line
+      if (buffer && buffer->length() != 0) {
+        if (!body(StringPiece(ch(buffer->data()), buffer->length()))) {
+          return false;
+        }
+      }
+      return true;
+    }
+  };
+
+  template<class Source,
+           class Value,
+           class Gen = Generator<Source>>
+  Gen compose(GenImpl<Value, Source>&& source) const {
+    return Gen(std::move(source.self()), delimiter_);
+  }
+
+  template<class Source,
+           class Value,
+           class Gen = Generator<Source>>
+  Gen compose(const GenImpl<Value, Source>& source) const {
+    return Gen(source.self(), delimiter_);
+  }
+};
+
+}  // namespace detail
+}  // namespace gen
+}  // namespace folly
+
diff --git a/folly/experimental/StringGen.h b/folly/experimental/StringGen.h
new file mode 100644
index 00000000..8eba7646
--- /dev/null
+++ b/folly/experimental/StringGen.h
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2012 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FOLLY_STRINGGEN_H_
+#define FOLLY_STRINGGEN_H_
+
+#include "folly/Range.h"
+
+namespace folly {
+namespace gen {
+
+namespace detail {
+class StringResplitter;
+}  // namespace detail
+
+/**
+ * Split the output from a generator into StringPiece "lines" delimited by
+ * the given delimiter.  Delimters are NOT included in the output.
+ *
+ * resplit() behaves as if the input strings were concatenated into one long
+ * string and then split.
+ */
+// make this a template so we don't require StringResplitter to be complete
+// until use
+template <class S=detail::StringResplitter>
+S resplit(char delimiter) {
+  return S(delimiter);
+}
+
+}  // namespace gen
+}  // namespace folly
+
+#include "folly/experimental/StringGen-inl.h"
+
+#endif /* FOLLY_STRINGGEN_H_ */
+
diff --git a/folly/experimental/test/GenBenchmark.cpp b/folly/experimental/test/GenBenchmark.cpp
index 18435c26..70db7be7 100644
--- a/folly/experimental/test/GenBenchmark.cpp
+++ b/folly/experimental/test/GenBenchmark.cpp
@@ -15,9 +15,13 @@
  */
 
 #include "folly/experimental/Gen.h"
+#include "folly/experimental/StringGen.h"
+#include "folly/experimental/FileGen.h"
 
-#include <glog/logging.h>
 #include <atomic>
+#include <thread>
+
+#include <glog/logging.h>
 
 #include "folly/Benchmark.h"
 
@@ -267,6 +271,86 @@ BENCHMARK_RELATIVE(Composed_GenRegular, iters) {
   folly::doNotOptimizeAway(s);
 }
 
+BENCHMARK_DRAW_LINE()
+
+namespace {
+
+const char* const kLine = "The quick brown fox jumped over the lazy dog.\n";
+const size_t kLineCount = 10000;
+std::string bigLines;
+const size_t kSmallLineSize = 17;
+std::vector<std::string> smallLines;
+
+void initStringResplitterBenchmark() {
+  bigLines.reserve(kLineCount * strlen(kLine));
+  for (size_t i = 0; i < kLineCount; ++i) {
+    bigLines += kLine;
+  }
+  size_t remaining = bigLines.size();
+  size_t pos = 0;
+  while (remaining) {
+    size_t n = std::min(kSmallLineSize, remaining);
+    smallLines.push_back(bigLines.substr(pos, n));
+    pos += n;
+    remaining -= n;
+  }
+}
+
+size_t len(folly::StringPiece s) { return s.size(); }
+
+}  // namespace
+
+BENCHMARK(StringResplitter_Big, iters) {
+  size_t s = 0;
+  while (iters--) {
+    s += from({bigLines}) | resplit('\n') | map(&len) | sum;
+  }
+  folly::doNotOptimizeAway(s);
+}
+
+BENCHMARK_RELATIVE(StringResplitter_Small, iters) {
+  size_t s = 0;
+  while (iters--) {
+    s += from(smallLines) | resplit('\n') | map(&len) | sum;
+  }
+  folly::doNotOptimizeAway(s);
+}
+
+BENCHMARK_DRAW_LINE()
+
+BENCHMARK(ByLine_Pipes, iters) {
+  std::thread thread;
+  int rfd;
+  int wfd;
+  BENCHMARK_SUSPEND {
+    int p[2];
+    CHECK_ERR(::pipe(p));
+    rfd = p[0];
+    wfd = p[1];
+    thread = std::thread([wfd, iters] {
+      char x = 'x';
+      PCHECK(::write(wfd, &x, 1) == 1);  // signal startup
+      FILE* f = fdopen(wfd, "w");
+      PCHECK(f);
+      for (int i = 1; i <= iters; ++i) {
+        fprintf(f, "%d\n", i);
+      }
+      fclose(f);
+    });
+    char buf;
+    PCHECK(::read(rfd, &buf, 1) == 1);  // wait for startup
+  }
+
+  auto s = byLine(rfd) | eachTo<int64_t>() | sum;
+  folly::doNotOptimizeAway(s);
+
+  BENCHMARK_SUSPEND {
+    ::close(rfd);
+    CHECK_EQ(s, int64_t(iters) * (iters + 1) / 2);
+    thread.join();
+  }
+}
+
 // Results from a dual core Xeon L5520 @ 2.27GHz:
 //
 // ============================================================================
@@ -300,6 +384,7 @@ BENCHMARK_RELATIVE(Composed_GenRegular, iters) {
 
 int main(int argc, char *argv[]) {
   google::ParseCommandLineFlags(&argc, &argv, true);
+  initStringResplitterBenchmark();
   runBenchmarks();
   return 0;
 }
diff --git a/folly/experimental/test/GenTest.cpp b/folly/experimental/test/GenTest.cpp
index 06499877..c3627831 100644
--- a/folly/experimental/test/GenTest.cpp
+++ b/folly/experimental/test/GenTest.cpp
@@ -20,7 +20,11 @@
 #include <set>
 #include <vector>
 #include "folly/experimental/Gen.h"
+#include "folly/experimental/StringGen.h"
+#include "folly/experimental/FileGen.h"
+#include "folly/experimental/TestUtil.h"
 #include "folly/FBVector.h"
+#include "folly/Format.h"
 #include "folly/dynamic.h"
 
 using namespace folly::gen;
@@ -30,6 +34,7 @@ using std::pair;
 using std::set;
 using std::unique_ptr;
 using std::vector;
+using std::string;
 using std::tuple;
 using std::make_tuple;
 //using std::unordered_map;
@@ -480,6 +485,34 @@ TEST(Gen, NoNeedlessCopies) {
   EXPECT_EQ(6, gen | take(3) | sum);
 }
 
+namespace {
+class TestIntSeq : public GenImpl<int, TestIntSeq> {
+ public:
+  TestIntSeq() { }
+
+  template <class Body>
+  bool apply(Body&& body) const {
+    for (int i = 1; i < 6; ++i) {
+      if (!body(i)) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  TestIntSeq(TestIntSeq&&) = default;
+  TestIntSeq& operator=(TestIntSeq&&) = default;
+  TestIntSeq(const TestIntSeq&) = delete;
+  TestIntSeq& operator=(const TestIntSeq&) = delete;
+};
+}  // namespace
+
+TEST(Gen, NoGeneratorCopies) {
+  EXPECT_EQ(15, TestIntSeq() | sum);
+  auto x = TestIntSeq() | take(3);
+  EXPECT_EQ(6, std::move(x) | sum);
+}
+
 TEST(Gen, FromArray) {
   int source[] = {2, 3, 5, 7};
   auto gen = from(source);
@@ -562,6 +595,98 @@ TEST(Gen, Dynamic) {
   EXPECT_EQ(dynamic(5), from(array3) | rconcat | rconcat | sum);
 }
 
+TEST(StringGen, EmptySplit) {
+  auto collect = eachTo<std::string>() | as<vector>();
+  {
+    auto pieces = from({""}) | resplit(',') | collect;
+    EXPECT_EQ(0, pieces.size());
+  }
+
+  // The last delimiter is eaten, just like std::getline
+  {
+    auto pieces = from({","}) | resplit(',') | collect;
+    EXPECT_EQ(1, pieces.size());
+    EXPECT_EQ("", pieces[0]);
+  }
+
+  {
+    auto pieces = from({",,"}) | resplit(',') | collect;
+    EXPECT_EQ(2, pieces.size());
+    EXPECT_EQ("", pieces[0]);
+    EXPECT_EQ("", pieces[1]);
+  }
+}
+
+TEST(StringGen, Split) {
+  auto collect = eachTo<std::string>() | as<vector>();
+  {
+    auto pieces = from({"hello,, world, goodbye, meow"}) |
+      resplit(',') | collect;
+    EXPECT_EQ(5, pieces.size());
+    EXPECT_EQ("hello", pieces[0]);
+    EXPECT_EQ("", pieces[1]);
+    EXPECT_EQ(" world", pieces[2]);
+    EXPECT_EQ(" goodbye", pieces[3]);
+    EXPECT_EQ(" meow", pieces[4]);
+  }
+  {
+    auto pieces = from({"hel", "lo,", ", world", ", goodbye, m", "eow"}) |
+      resplit(',') | collect;
+    EXPECT_EQ(5, pieces.size());
+    EXPECT_EQ("hello", pieces[0]);
+    EXPECT_EQ("", pieces[1]);
+    EXPECT_EQ(" world", pieces[2]);
+    EXPECT_EQ(" goodbye", pieces[3]);
+    EXPECT_EQ(" meow", pieces[4]);
+  }
+}
+
+TEST(FileGen, ByLine) {
+  auto collect = eachTo<std::string>() | as<vector>();
+  test::TemporaryFile file("ByLine");
+  static const std::string lines(
+      "Hello world\n"
+      "This is the second line\n"
+      "\n"
+      "\n"
+      "a few empty lines above\n"
+      "incomplete last line");
+  EXPECT_EQ(lines.size(), write(file.fd(), lines.data(), lines.size()));
+
+  auto expected = from({lines}) | resplit('\n') | collect;
+  auto found = byLine(file.path().c_str()) | collect;
+
+  EXPECT_TRUE(expected == found);
+}
+
+class FileGenBufferedTest : public ::testing::TestWithParam<int> { };
+
+TEST_P(FileGenBufferedTest, FileWriter) {
+  size_t bufferSize = GetParam();
+  test::TemporaryFile file("FileWriter");
+
+  static const std::string lines(
+      "Hello world\n"
+      "This is the second line\n"
+      "\n"
+      "\n"
+      "a few empty lines above\n");
+
+  auto src = from({lines, lines, lines, lines, lines, lines, lines, lines});
+  auto collect = eachTo<std::string>() | as<vector>();
+  auto expected = src | resplit('\n') | collect;
+
+  src | eachAs<StringPiece>() | toFile(file.fd(), bufferSize);
+  auto found = byLine(file.path().c_str()) | collect;
+
+  EXPECT_TRUE(expected == found);
+}
+
+INSTANTIATE_TEST_CASE_P(
+    DifferentBufferSizes,
+    FileGenBufferedTest,
+    ::testing::Values(0, 1, 2, 4, 8, 64, 4096));
+
 int main(int argc, char *argv[]) {
   testing::InitGoogleTest(&argc, argv);
   google::ParseCommandLineFlags(&argc, &argv, true);