The standard doesn’t quite spell it out, but v.erase(q) is defined, “Erases the element pointed to by q” in [sequence.reqmts]. This means that q must actually point to an element, which the end iterator doesn’t. Passing in the end iterator is undefined behavior. Unfortunately, you need to write: auto it = std::find(…); if (it != … Read more
The performance difference is likely negligable or none (the compiler might optimise them to be identical); you should worry about other things, like whether your program is correct (a slow but correct program is better than a fast and incorrect program). There are other advantages to using iterators though, such as being able to change … Read more
Below is a simple implementation of module spam with one function myiter(int) returning iterator: import spam for i in spam.myiter(10): print i prints numbers from 0 to 9. It is simpler then your case but shows main points: defining object with standard __iter__() and next() methods, and implementing iterator behaviour including raising StopIteration when appropriate. … Read more
I’m not sure if this is quite an answer to your questions but hopefully it explains a bit about the difference between Python 2 and 3 in this regard. In Python 2, iter(d.keys()) and d.iterkeys() are not quite equivalent, although they will behave the same. In the first, keys() will return a copy of the … Read more
You can only use yield return in a function that returns an IEnumerable or an IEnumerator, not a List<T>. You need to change your function to return an IEnumerable<DesktopComputer>. Alternatively, you can rewrite the function to use List<T>.ConvertAll: return GetComputerIdTags().ConvertAll(pcTag => new DesktopComputer() { AssetTag = pcTag, Description = “PC ” + pcTag, AcquireDate = … Read more
The two versions are not the same though. In the second version it compares the iterator against list.end() every time, and what list.end() evaluates to might change over the course of the loop. Now of course, you cannot modify list through the const_iterator it; but nothing prevents code inside the loop from just calling methods … Read more
One solution would be a list comprehension and the slice operator: with open(filename, ‘r’) as infile: lines = [line for line in infile][:N] After this lines is tuple of lines. However, this would load the complete file into memory. If you don’t want this (i.e. if the file could be really large) there is another … Read more
There are lots of ways you could mean this. If you just want to panic, use .map(|x| x.unwrap()). If you want all results or a single error, collect into a Result<X<T>>: let results: Result<Vec<i32>, _> = result_i32_iter.collect(); If you want everything except the errors, use .filter_map(|x| x.ok()) or .flat_map(|x| x). If you want everything up … Read more
There is nothing really wrong, but it will certainly limit the use of the template. You won’t be able to just put an iterator returned by something else or generated like v.begin(), since those will be temporaries. You will always first have to make a local copy, which is some kind of boilerplate not really … Read more
typename std::iterator_traits<Iter>::value_type This will work if your template is instantiated with Iter as a pointer type. By the way, typename isn’t part of the type itself. It tells the compiler that value_type really is a type. If it were the name of a function or a static data member, then that affects the syntax. The … Read more