lazy-evaluation

Lazy Filtering CSV Files I had the need to filter through millions of log records, stored as numerous CSV files. The size of the records greatly exceeded my available memory so I wanted to go with a lazy approach. Java 8 Streams API With jdk8 we have the Streams API which paired with Apache commons-csv allows us to easily accomplish this. public class LazyFilterer { private static Iterable<CSVRecord> getIterable(String fileName) throws IOException { return CSVFormat .DEFAULT .withFirstRecordAsHeader() .parse(new BufferedReader(new FileReader(fileName))); } public static void main(String[] args

This question is the opposite of an existing question " Can the use of C++11's 'auto' improve performance? " One of the answers to that question indicated that usage of auto can have not only positive but also negative effects. I believe we need a separate question, with answers focusing on that side of auto . Leon With auto there is no conversion at the variable declaration+initialization line. But if such conversion must happen anyway, it better happen once during initialization than multiple times later. struct X { ... }; struct Y { operator X() const; ... }; Y foo(); // maybe, originally

I'll give a simplified example here. Suppose I have an iterator in python, and each object that this iterator returns is itself iterable. I want to take all the objects returned by this iterator and chain them together into one long iterator. Is there a standard utility to make this possible? Here is a contrived example. x = iter([ xrange(0,5), xrange(5,10)]) x is an iterator that returns iterators, and I want to chain all the iterators returned by x into one big iterator. The result of such an operation in this example should be equivalent to xrange(0,10), and it should be lazily evaluated.

I know that in Matlab, there is a 'lazy' evaluation when a new variable is assigned to an existing one. Such as: array1 = ones(1,1e8); array2 = array1; The value of array1 won't be copied to array2 unless the element of array2 is modified. From this I supposed that all the variables in Matlab are actually value-type and are all passed by values (although lazy evaluation is used). This also implies that the variables are created on the call stack. Well, I am not judging the way it treats the variables, although I have never seen a second programming language doing this way. I mean, for possibly