CppStreams

CppStreams is a data pipeline library for C++14.

Example:

using namespace cpp_streams;

std::vector<int> ints {3,1,4,1,5,9,2,6,5,4};

// Produce a sum of even ints (+1)
auto sum =
      from (ints)
  >>  filter ([] (auto && v) {return v % 2 == 0;})  // Keep only even numbers
  >>  map ([] (auto && v) {return v + 1;})          // +1
  >>  to_sum                                        // Compute sum
  ;

std::cout << "SUM: " << sum << std::endl;

Verified compilers

Visual Studio 2015
G++ 4.9.2
Clang++ 3.6.0

Motivation

In functional programming languages, such as Haskell & SML, programmers have been working with data pipelines for 30+ years.

"Recently" this has become available to mainstream programmers in languages such as C# (2008, LINQ) and Java (2014, Streams) as these languages has begun adopting more functional constructs.

With C++11 C++ got lambda expressions which is crucial in order to implement data pipelines. Several attempts have been made to implement data pipelines among others cpplinq that I begun working on during summer 2012.

The motivation for CppStreams are:

Use push instead of pull as this seems to lead to more efficient pipelines.
Support of update of source container (cpplinq can't do this)
Use C++14 in order to make the library code more succinct and easier to extend.
Use functional naming conventions over C# LINQ naming conventions.
Having a bit of fun

Inspiration

C# LINQ got me interested in data pipelines
F# made me to rediscover FP
nessos/Streams is a data pipeline for F#/C# that relies on push
Even though I authored cpplinq it's still an inspiration for CppStreams in terms of goals and learning on what can be improved

Status

Source operators

- Currently doesn't work on VS2015 RC

Prio	Status	Source operator	Comment
	Done	from	Creates a source from a STL container
	Done	from_iterators	Creates a source from a pair of iterators
	Done	from_array	Creates a source from a C-style array
	Done	from_repeat	Creates an source from a value and repeat count
	Done	from_singleton	Creates an source from a value
	Done	from_empty	Creates an empty source
	Done	from_range*	Creates a source from a range
2	Planned	from_unfold	Creates an source from an unfold function
2	Planned	from_generator	Creates an source from a generator function

Pipe operators

Prio	Status	Pipe operator	Comment
	Done	filter	Filter elements in pipeline using filter function
	Done	map	Maps elements in pipeline using map function
	Done	reverse*	Reverses elements in pipeline
	Done	append	Appends two pipelines
	Done	skip_while	Skips while func is true for elements in pipeline
	Done	take_while	Takes while func is true for elements in pipeline
	Done	mapi	Maps elements in pipeline using mapi function
	Done	collect	Collects sub elements in pipeline
	Done	skip	Skips n elements in pipeline
	Done	take	Takes n elements in pipeline
	Done	sort*	Orders elements in pipeline using order function
	Done	sort_by*	Orders elements in pipeline using order function
1	Planned	order_by	Orders elements in pipeline using order function
1	Planned	then_by	Orders elements in pipeline using order function
1	Planned	concat	Concats a pipeline of pipelines
2	Planned	choose	Chooses elements in pipeline
2	Planned	distinct_by	Unique elements in pipeline using select function
2	Planned	partition	Partitions elements in pipeline in two heaps
2	Planned	reduce	Reduces elements in pipeline using reduce function
2	Planned	union_with	Union of two pipelines
2	Planned	intersect_with	Intersection of two pipelines
2	Planned	expect_with	Disjunction of two pipelines
2	Planned	windowed	Splits elements in pipeline in chunks
2	Planned	compare_with	Compares two pipelines
2	Planned	pairwise	Makes pair of elements in pipeline
2	Planned	permute	Permutes elements in pipeline using permutes func
2	Planned	join_with	Joins two pipelines

Sink operators

Prio	Status	Sink operator	Comment
	Done	to_first_or_default	Returns the first element of pipeline or default
	Done	to_last_or_default	Returns the last element of pipeline or default
	Done	to_sum	Returns sum of elements in pipeline
	Done	to_vector	Returns vector of elements in pipeline
	Done	to_iter	Applies iteration function to elements in pipeline
	Done	to_fold	Applies fold function to elements in pipeline
	Done	to_any	True if pipeline has any element matching predicate
	Done	to_all	True if all pipeline element matches predicate
	Done	to_length	Returns length of elements in pipeline
	Done	to_set	Returns set of elements in pipeline
	Done	to_map*	Returns map of elements in pipeline
	Done	to_max	Returns max of elements in pipeline
	Done	to_min	Returns min of elements in pipeline
2	Planned	to_average	Returns average of elements in pipeline
2	Planned	to_first	Returns the first element of pipeline or empty
2	Planned	to_split_at	Splits a pipeline at index n
2	Planend	to_last	Returns the last element of pipeline or empty
2	Planned	to_lookup	Returns lookup of elements in pipeline
2	Planned	to_scan	Applies scan function to elements in pipeline
2	Planned	to_split_into	Splits a pipeline into at most n chunks

TODO

NEXT: 011

010 - VS2015: Find work-around for busted pipes
006 - performance: Add performance tests
007 - coverage: Add code coverage tests
001 - general: Capture by RValue reference as implied here: capture-by-universal-reference
002 - iteration_sink: Check return type, if void return false
008 - general: Use static_assert to check argument types
009 - general: Use std::forward in API functions
003 - from: Should capture the container by value if RValue reference
004 - test: Figure out how to test negative type test cases (these will trigger compilation errors).
005 - general: Not happy with the requirement to capture this in lambdas, find alternative

Done

000 - Complete status of operators

mrange/CppStreams