Multiple readers, no writers is okay: https://groups.google.com/d/msg/golang-nuts/HpLWnGTp-n8/hyUYmnWJqiQJ One writer, no readers is okay. (Maps wouldn’t be much good otherwise.) Otherwise, if there is at least one writer and at least one more either writer or reader, then all readers and writers must use synchronization to access the map. A mutex works fine for this.
I use a functor object to calculate hash of enum class: struct EnumClassHash { template <typename T> std::size_t operator()(T t) const { return static_cast<std::size_t>(t); } }; Now you can use it as 3rd template-parameter of std::unordered_map: enum class MyEnum {}; std::unordered_map<MyEnum, int, EnumClassHash> myMap; So you don’t need to provide a specialization of std::hash, the … Read more
You’re looking for the .filter() function: $scope.appIds = $scope.applicationsHere.filter(function(obj) { return obj.selected; }); That’ll produce an array that contains only those objects whose “selected” property is true (or truthy). edit sorry I was getting some coffee and I missed the comments – yes, as jAndy noted in a comment, to filter and then pluck out … Read more
You can use Map.fromIterable: var result = Map.fromIterable(l, key: (v) => v[0], value: (v) => v[1]); or collection-for (starting from Dart 2.3): var result = { for (var v in l) v[0]: v[1] };
These two classes vary in a few ways. ConcurrentHashMap does not guarantee* the runtime of its operations as part of its contract. It also allows tuning for certain load factors (roughly, the number of threads concurrently modifying it). ConcurrentSkipListMap, on the other hand, guarantees average O(log(n)) performance on a wide variety of operations. It also … Read more
A Map maps something to something else. I like to use names like uidToPerson. “To” being the shortest unambiguous way I can think of to show that I have a map. Edit: I’ll add that I prefer to have the map named this way, because “key” and “value” appear in that order in the name. … Read more
Basically, it allows you to do this: callAPIThatTakesAMap(Collections.singletonMap(key, value)); rather than this: Map<KeyType, ValueType> m = new HashMap<KeyType, ValueType>(); m.put(key, value); callAPIThatTakesAMap(m); which is much nicer when you only have a single key/value pair. This situation probably does not arise very often, but singleton() and singletonList() can quite frequently be useful.
TL;DR go directly to the final example I’ll try and recap. Definitions The for comprehension is a syntax shortcut to combine flatMap and map in a way that’s easy to read and reason about. Let’s simplify things a bit and assume that every class that provides both aforementioned methods can be called a monad and … Read more
For Googlers that don’t expect duplicates or are fine with the default duplicate handling policy: List(“a” -> 1, “b” -> 2, “a” -> 3).toMap // Result: Map(a -> 3, c -> 2) As of 2.12, the default policy reads: Duplicate keys will be overwritten by later keys: if this is an unordered collection, which key … Read more
If you have a map object like this: var mapObject = new google.maps.Map(document.getElementById(“map”), _mapOptions); use mapObject.getZoom();