You cannot do this because it would allow you to circumvent runtime checks for uniqueness violations. RefCell provides you a way to “defer” mutability exclusiveness checks to runtime, in exchange allowing mutation of the data it holds inside through shared references. This is done using RAII guards: you can obtain a guard object using a … Read more
The term “consume” is an informal term that refers to the way iterators work in Python. An “iterator” is a single object that is responsible for creating some sequence of elements. This sequence might be elements of an existing list, or it might be something calculated, like prime numbers or the decimal digits of π. … Read more
This is a case for Higher Ranked Trait Bounds (HRTB). The point is that you do not want &L to implement IntoIterator<Item = &T> for one lifetime but for all potential lifetimes that L may happen to have. In this case, you need to use a Higher Ranked Trait Bound: for<‘a> will take care of … Read more
You can use GMan’s answer — but the question is, why do you want to use std::copy? You should use the member function std::map<k, v>::insert instead. m2.insert(m1.begin(), m1.end());
There is no way to write this with a loop statement. async/await code always executes sequentially, to do things concurrently you need to use promise combinators directly. For plain promises, there’s Promise.all, for async iterators there is nothing (yet) so we need to write it on our own: async function* combine(iterable) { const asyncIterators = … Read more
You need to be careful because erase() will invalidate existing iterators. However, it will return a new valid iterator you can use: for ( it = Entities.begin(); it != Entities.end(); ) { if( (*it)->getXPos() > 1.5f ) { delete * it; it = Entities.erase(it); } else { ++it; } }
Although your question is not very clear, I’m going to assume you mean a 2D vector to mean a vector of vectors: vector< vector<int> > vvi; Then you need to use two iterators to traverse it, the first the iterator of the “rows”, the second the iterators of the “columns” in that “row”: //assuming you … Read more
Original answer The rationale is given in N4284, which is the adopted version of the contiguous iterators proposal: This paper introduces the term “contiguous iterator” as a refinement of random-access iterator, without introducing a corresponding contiguous_iterator_tag, which was found to break code during the Issaquah discussions of Nevin Liber’s paper N3884 “Contiguous Iterators: A Refinement … Read more
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
name_map = {‘oldcol1’: ‘newcol1’, ‘oldcol2’: ‘newcol2’, ‘oldcol3’: ‘newcol3’…} for row in rows: # Each row is a dict of the form: {‘oldcol1’: ‘…’, ‘oldcol2’: ‘…’} row = dict((name_map[name], val) for name, val in row.iteritems()) … Or in Python2.7+ with Dict Comprehensions: for row in rows: row = {name_map[name]: val for name, val in row.items()}