It is possible to get functionality similar to .NET's LINQ in C++?

It is possible to get functionality similar to .NET's LINQ in C++? Would this require language extensions or could it be done using some very clever macros? Or even through a to开发者_StackOverflow中文版ol like Qt's moc (meta-object compiler)? Are there any existing LINQ implementations for C++ and if so, what are they?

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Check CLinq (here and here) or Linq++ (here). Also try p-stade (here); however, it uses the STL and it doesn't have the same interface as LINQ, but it's pretty complete.

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With this Linq library for C++11, you can do list comprehension using linq-like syntax:

std::vector<int> numbers = { 1, 2, 3, 4 };
auto r = LINQ(from(x, numbers) where(x > 2) select(x * x));
for (auto x : r) printf("%i\n", x);

It uses the preprocessor to parse out the from, where, and select clauses, and converts it to the equivalent of this using Boost.Range adaptors:

auto r = numbers 
        | boost::adaptors::filtered([](int x) { return x > 2; }) 
        | boost::adaptors::transformed([](int x) { return x * x; });

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It is possible to get functionality similar to .NET's LINQ in C++? Would this require language extensions or could it be done using some very clever macros?

C++ macros aren't powerful enough to implement something as complex as LINQ.

To implement LINQ-like system in the form of library, the language needs:

• Good embedded-DSL capabilities.
• Lazy evaluation
• Persistent collections
• Lambda expressions

Embedded DSLs in C++ look very ugly thanks to the rigorous syntax and semantics of the language (for example, look at Boost.Spirit and then look at an equivalent library from a DSL-friendly language like Haskell). You can get lazy evaluation via boost::phoenix. There is no persistent collections library available for C++ (apart from FC++, which is pretty incomplete). Lambda Expressions are coming to C++ in the next standard of the language.

Even if someday someone manages to create a LINQ-like system for C++ using above-mentioned ingredients, that system won't be as good as LINQ in .NET. So yes, it is possible, but not very practical. :)

Or even through a tool like Qt's moc (meta-object compiler)?

This is very much possible. But then it won't still really be C++, will it? ;)

Are there any existing LINQ implementations for C++ and if so, what are they?

A few attempts have been made in this direction (as pointed out by other gentleman here). None of them comes close to the "real" LINQ, but they're still worth having a look at. :)

EDIT:
Apparently I was wrong about the "practical" bit. Look at the p-stade link in Yassin's answer, which is a great example of what can be achieved with clever use of powerful C++ abstractions. :-)