To understand the keyof typeof usage in TypeScript, first you need to understand what are literal types and union of literal types. So, I’ll explain these concepts first and then explain keyof and typeof individually in detail. After that, I’ll come back to enum to answer what is asked in the question. It’s a long … Read more
The reason you’re seeing “string” returned in your first loop is that num refers to the array index, not the value of numarray at that index. Try changing your first loop to alert num instead of typeof num and you’ll see that it spits out 0, 1, and 2, which are the indicies and not … Read more
There’s very little practical use for String objects as created by new String(“foo”). The only advantage a String object has over a primitive string value is that as an object it can store properties: var str = “foo”; str.prop = “bar”; alert(str.prop); // undefined var str = new String(“foo”); str.prop = “bar”; alert(str.prop); // “bar” … Read more
Try the following: int i = 20; float f = 20.2f; System.out.println(((Object)i).getClass().getName()); System.out.println(((Object)f).getClass().getName()); It will print: java.lang.Integer java.lang.Float As for instanceof, you could use its dynamic counterpart Class#isInstance: Integer.class.isInstance(20); // true Integer.class.isInstance(20f); // false Integer.class.isInstance(“s”); // false
You can use the typeid operator: #include <typeinfo> … cout << typeid(variable).name() << endl;
Angus Croll recently wrote an interesting blog post about this – http://javascriptweblog.wordpress.com/2011/08/08/fixing-the-javascript-typeof-operator/ He goes through the pros and cons of the various methods then defines a new method ‘toType’ – var toType = function(obj) { return ({}).toString.call(obj).match(/\s([a-zA-Z]+)/)[1].toLowerCase() }
Since typeof is a compiler extension, there is not really a definition for it, but in the tradition of C it would be an operator, e.g sizeof and _Alignof are also seen as an operators. And you are mistaken, C has dynamic types that are only determined at run time: variable modified (VM) types. size_t … Read more
Use instanceof for custom types: var ClassFirst = function () {}; var ClassSecond = function () {}; var instance = new ClassFirst(); typeof instance; // object typeof instance == ‘ClassFirst’; // false instance instanceof Object; // true instance instanceof ClassFirst; // true instance instanceof ClassSecond; // false Use typeof for simple built in types: ‘example … Read more
See another answer; this feature now exists in C# I usually use a dictionary of types and delegates. var @switch = new Dictionary<Type, Action> { { typeof(Type1), () => … }, { typeof(Type2), () => … }, { typeof(Type3), () => … }, }; @switch[typeof(MyType)](); It’s a little less flexible as you can’t fall through … Read more
The type of a lambda expression is unspecified. But they are generally mere syntactic sugar for functors. A lambda is translated directly into a functor. Anything inside the [] are turned into constructor parameters and members of the functor object, and the parameters inside () are turned into parameters for the functor’s operator(). A lambda … Read more