truthiness

I just want to use Null Object Design Pattern, but I found I can inherit from NilClass. I can write a method "nil?" and return false but what if user write code below if null_object puts "shouldn't be here" end For clarify what I try to do is: record = DB.find(1) # if it can not find record 1, the bellow code should not raise exception record.one_attr # and what's more if record puts "shouldn't be here" end # I don't want to override all NilClass An approach that may work for you is to overide the method #nil? in your Null object. This means that in your code to test for null you have to use

This question already has an answer here: Assigning (instead of defining) a __getitem__ magic method breaks indexing [duplicate] 2 answers The documentation clearly states that When this method ( __bool__ ) is not defined, __len__() is called, if it is defined, and the object is considered true if its result is nonzero. If a class defines neither __len__() nor __bool__() , all its instances are considered true. Bold is my insertion, italics is mine but the text is actually there. The fact that the class must contain the method is readily tested by class A: pass a = A() a.__bool__ = (lamda self

I've been reading about JavaScript hoisting sometime back. JavaScript Scoping and Hoisting by Ben Cherry Two words about “hoisting” by Dmitry Soshnikov and, some more about JavaScript type-coercion, truth & false test: Truth, Equality and JavaScript and some other resource And while practicing some, and found I m missing some important concept about the hoisting and a variable' truthy & falsy. 1: 'if' truth test with duplicate variable declaration var foo = 1; function bar() { if (!foo) { alert('inside if'); var foo = 10; } } bar(); o/p: inside if Doubt: 'foo' value being '1', if(!foo) should

In IE and Chrome, typing this into the JavaScript console throws an exception: {} == false // "SyntaxError: Unexpected token ==" However, all of these statements are evaluated with no problem: false == {} // false ({} == false) // false var a = {}; a == false // false Is this intentional behavior? Why does this happen? In the console, when you start a statement with {} , you are not creating an object literal, but a code block (i.e. the same block as you would make with an if statement or a loop body). A symbol like == is then obviously not expected afterwards. If you think of a code block,

I was expecting the following comparison to give an error: var A = B = 0; if(A == B == 0) console.log(true); else console.log(false); but strangely it returns false . Even more strangely, console.log((A == B == 1)); returns true . How does this "ternary" kind of comparison work? First, we need to understand that a == comparison between a number and a boolean value will result in internal type conversion of Boolean value to a number ( true becomes 1 and false becomes 0 ) The expression you have shown is evaluated from left to right. So, first A == B is evaluated and the result is true and you