boolean-logic

I can't understand the logic behind the terms union types and intersection types in TypeScript. Pragmatically, if the properties of different types are sets of properties, if I combine them with the & operator, the resulting type will be the union of the of those sets. Following that logic, I would expect types like this to be called union types . If I combine them with | , I can only use the common properties of them, the intersection of the sets. Wikipedia seems to back that logic: The power set (set of all subsets) of any given nonempty set S forms a Boolean algebra, an algebra of sets,

I have a $name variable containing a string, and when I test it, I never get the "Name should be between 2 and 40 characters" error even when it's less than 2 characters long or more than 40. Why? if (strlen($name) < 2 && strlen($name) > 40) { $nameError = 'Name should be between 2 and 40 characters'; } T.J. Crowder How can the length be less than 2 and greater than 40? You want || ("or"), not && ("and"). if (strlen($name) < 2 || strlen($name) > 40) { // -------------------^^ 来源： https://stackoverflow.com/questions/42190142/whats-wrong-with-my-if-else-statement

For some reason this function confused me: def protocol(port): return port == "443" and "https://" or "http://" Can somebody explain the order of what's happening behind the scenes to make this work the way it does. I understood it as this until I tried it: Either A) def protocol(port): if port == "443": if bool("https://"): return True elif bool("http://"): return True return False Or B) def protocol(port): if port == "443": return True + "https://" else: return True + "http://" Is this some sort of special case in Python, or am I completely misunderstanding how statements work? It's an old

Suppose I have the following expression String myString = getStringFromSomeExternalSource(); if (myString != null && myString.trim().length() != 0) { ... } Eclipse warns me that myString might be null in the second phrase of the boolean expression. However, I know some that some compilers will exit the boolean expression entirely if the first condition fails. Is this true with Java? Or is the order of evaluation not guaranteed? However, I know some that some compilers will exit the boolean expression entirely if the first condition fails. Is this true with Java? Yes, that is known as Short

I had to replace the default underscore teplating delimiters/Interpolate regex for compatibility with asp.net webforms.From the website i opted for mustache like syntax _.templateSettings = { interpolate : /\{\{(.+?)\}\}/g }; tried this _.template("{{if(loggedIn)Welcome {{name}}}}",{name:"James",completed:true}); but seems this is not the way( since a error occurred) to check boolean expression using a templating system. But from the docs seems it is possible as well as execute arbitrary JavaScript code, with <% … %> So how do i execute arbitrary js code with the above mentioned interpolation

I've got some dynamically-generated boolean logic expressions, like: (A or B) and (C or D) A or (A and B) A empty - evaluates to True The placeholders get replaced with booleans. Should I, Convert this information to a Python expression like True or (True or False) and eval it? Create a binary tree where a node is either a bool or Conjunction / Disjunction object and recursively evaluate it? Convert it into nested S-expressions and use a Lisp parser? Something else? Suggestions welcome. It shouldn't be difficult at all to write a evaluator that can handle this, for example using pyparsing .