Determine if a string contains only alphanumeric characters (or a space)
Looks good to me, but you can use isalnum(c) instead of isalpha and isdigit.
iterator
How to iterate over a WeakMap?
Is it possible to nevertheless loop over entries in some way? No, as you say, the contents of a WeakMap are not accessible by design, and there is no iterability. If not … how does the Chrome console do this? The console uses the debugging API of the JS engine, which allows access to the … Read more
How do I return a Filter iterator from a function?
Rust 1.26 fn filter_one(input: &[u8]) -> impl Iterator<Item = &u8> { input.iter().filter(|&&x| x == 1) } fn main() { let nums = vec![1, 2, 3, 1, 2, 3]; let other: Vec<_> = filter_one(&nums).collect(); println!(“{:?}”, other); } Rust 1.0 fn filter_one<‘a>(input: &’a [u8]) -> Box<Iterator<Item = &’a u8> + ‘a> { Box::new(input.iter().filter(|&&x| x == 1)) } … Read more
Python equivalents to LINQ
The following Python lines should be equivalent to what you have (assuming func, or lambda in your code, returns a Boolean): # Any contains = any(func(x) for x in enumerable) # Count count = sum(func(x) for x in enumerable) # Distinct: since we are using a custom comparer here, we need a loop to keep … Read more
Do STL iterators guarantee validity after collection was changed?
Depends on the container. e.g. if it’s a vector, after modifying the container all iterators can be invalidated. However, if it’s a list, the iterators irrelevant to the modified place will remain valid. A vector’s iterators are invalidated when its memory is reallocated. Additionally, inserting or deleting an element in the middle of a vector … Read more
How can I iterate over two vectors simultaneously using BOOST_FOREACH?
Iterating over two things simultaneously is called a “zip” (from functional programming), and Boost has a zip iterator: The zip iterator provides the ability to parallel-iterate over several controlled sequences simultaneously. A zip iterator is constructed from a tuple of iterators. Moving the zip iterator moves all the iterators in parallel. Dereferencing the zip iterator … Read more
Incrementing iterators: Is ++it more efficient than it++? [duplicate]
The reason behind the preincrement being faster is that post-increment has to make a copy of the old value to return. As GotW #2 put it, “Preincrement is more efficient than postincrement, because for postincrement the object must increment itself and then return a temporary containing its old value. Note that this is true even … Read more
Closing a java.util.Iterator
Create a custom iterator which implement the AutoCloseable interface public interface CloseableIterator<T> extends Iterator<T>, AutoCloseable { } And then use this iterator in a try with resource statement. try(CloseableIterator iterator = dao.findAll()) { while(iterator.hasNext()){ process(iterator.next()); } } This pattern will close the underlying resource whatever happens: – after the statement complete – and even if … Read more
Iterators in C++ (stl) vs Java, is there a conceptual difference?
Perhaps a bit more theoretical. Mathematically, collections in C++ can be described as a half-open interval of iterators, namely one iterator pointing to the start of the collection and one iterator pointing just behind the last element. This convention opens up a host of possibilities. The way algorithms work in C++, they can all be … Read more
Java: how to get Iterator from String [duplicate]
One option is to use Guava: ImmutableList<Character> chars = Lists.charactersOf(someString); UnmodifiableListIterator<Character> iter = chars.listIterator(); This produces an immutable list of characters that is backed by the given string (no copying involved). If you end up doing this yourself, though, I would recommend not exposing the implementation class for the Iterator as a number of other … Read more