Finally found the real answer: http://tc39wiki.calculist.org/es6/weak-map/ A key property of Weak Maps is the inability to enumerate their keys. This is necessary to prevent attackers observing the internal behavior of other systems in the environment which share weakly-mapped objects. Should the number or names of items in the collection be discoverable from the API, even … Read more
Not in ruby but in ActiveSupport: characters = [“Konata”, “Kagami”, “Tsukasa”] “Konata”.in?(characters) # => true
each is different from map and collect, but map and collect are the same (technically map is an alias for collect, but in my experience map is used a lot more frequently). each performs the enclosed block for each element in the (Enumerable) receiver: [1,2,3,4].each {|n| puts n*2} # Outputs: # 2 # 4 # … Read more
You add: using System.Linq; at the top of your source and make sure you’ve got a reference to the System.Core assembly. Count() is an extension method provided by the System.Linq.Enumerable static class for LINQ to Objects, and System.Linq.Queryable for LINQ to SQL and other out-of-process providers. EDIT: In fact, using Count() here is relatively inefficient … Read more
ar = [{“Vegetable”=>10}, {“Vegetable”=>5}, {“Dry Goods”=>3}, {“Dry Goods”=>2}] p ar.inject{|memo, el| memo.merge( el ){|k, old_v, new_v| old_v + new_v}} #=> {“Vegetable”=>15, “Dry Goods”=>5} Hash.merge with a block runs the block when it finds a duplicate; inject without a initial memo treats the first element of the array as memo, which is fine here.
An enumerable property is one that can be included in and visited during for..in loops (or a similar iteration of properties, like Object.keys()). If a property isn’t identified as enumerable, the loop will ignore that it’s within the object. var obj = { key: ‘val’ }; console.log(‘toString’ in obj); // true console.log(typeof obj.toString); // “function” … Read more
It’s certainly not a bug. It’s behaving exactly as documented: true if every element of the source sequence passes the test in the specified predicate, or if the sequence is empty; otherwise, false. Now you can argue about whether or not it should work that way (it seems fine to me; every element of the … Read more
AsEnumerable() is effectively a cast to IEnumerable<T>, which makes member resolution find members of Enumerable instead of Queryable. It’s usually used when you want to force part of a query to run as SQL (or similar), and the remainder to run using LINQ to Objects. See my Edulinq blog post on it for more information. … Read more
The Zip operator merges the corresponding elements of two sequences using a specified selector function. var letters= new string[] { “A”, “B”, “C”, “D”, “E” }; var numbers= new int[] { 1, 2, 3 }; var q = letters.Zip(numbers, (l, n) => l + n.ToString()); foreach (var s in q) Console.WriteLine(s); Ouput A1 B2 C3
Array#each executes the given block for each element of the array, then returns the array itself. Array#map also executes the given block for each element of the array, but returns a new array whose values are the return values of each iteration of the block. Example: assume you have an array defined thusly: arr = … Read more