Tutorial by Examples: boolean

A boolean represents the most basic datatype in TypeScript, with the purpose of assigning true/false values. // set with initial value (either true or false) let isTrue: boolean = true; // defaults to 'undefined', when not explicitely set let unsetBool: boolean; // can ...

We define the type of boolean expressions whose atoms are identified by strings as type expr = | Atom of string | Not of expr | And of expr * expr | Or of expr * expr and can evaluate these expressions using an oracle : string -> bool giving the values of the atoms we find as follows: le...

Booleans and other values When dealing with lua it is important to differentiate between the boolean values true and false and values that evaluate to true or false. There are only two values in lua that evaluate to false: nil and false, while everything else, including the numerical 0 evaluate to...

Actually any value different from NIL is considered a true value in Common Lisp. For instance: CL-USER> (let ((a (+ 2 2))) (if a a "Oh my! 2 + 2 is equal to NIL!")) 4 This fact can be combined with the boolean operators to make programs m...

With the ~ selector, you can easily implement a global accessible boolean without using JavaScript. Add boolean as a checkbox To the very beginning of your document, add as much booleans as you want with a unique id and the hidden attribute set: <input type="checkbox" id="sideba...

Dim Value As Boolean A Boolean is used to store values that can be represented as either True or False. Internally, the data type is stored as a 16 bit value with 0 representing False and any other value representing True. It should be noted that when a Boolean is cast to a numeric type, all of...

If you get an error like this: Fatal error: Call to a member function fetch_assoc() on boolean in C:\xampp\htdocs\stack\index.php on line 7 Other variations include something along the lines of: mysql_fetch_assoc() expects parameter 1 to be resource, boolean given... These errors mean that t...

Converter between boolean and visibility. Get bool value on input and returns Visibility value. NOTE: This converter have already exists in System.Windows.Controls namespace. public sealed class BooleanToVisibilityConverter : IValueConverter { /// <summary> /// Convert bool or Nu...

All integers or pointers can be used in an expression that is interpreted as "truth value". int main(int argc, char* argv[]) { if (argc % 4) { puts("arguments number is not divisible by 4"); } else { puts("argument number is divisible by 4"); } ... ...

Python 2.x2.7 In Python 2, if you want to define a class boolean value by yourself, you need to implement the __nonzero__ method on your class. The value is True by default. class MyClass: def __nonzero__(self): return False my_instance = MyClass() print bool(MyClass) # Tru...

Returns true or false, which indicates whether the regexp is matched or not without updating $~ and other related variables. If the second parameter is present, it specifies the position in the string to begin the search. /R.../.match?("Ruby") #=> true /R.../.match?("Ruby&quot...

Any value in Clojure is considered truthy unless it is false or nil. You can find the truthiness of a value with (boolean value). You can find the truthiness of a list of values using (or), which returns true if any arguments are truthy, or (and) which returns true if all arguments are truthy. =&gt...

you can custom class below one private final String PROTOCOL_CONTENT_TYPE = String.format("application/json; charset=%s", PROTOCOL_CHARSET); public BooleanRequest(int method, String url, String requestBody, Response.Listener<Boolean> listener, Response.ErrorListener errorList...

CREATE TABLE all_binary_types( c_boolean boolean, c_binary binary ); Sample data: insert into all_binary_types values (0,1234); insert into all_binary_types values (1,4321); Note: For boolean, internally it stored as true or false. For binary, it will store base64 encoded value....

for numbers, a zero value evaluates to false, non zero to true int i = 0 ... if (i) print "some ${i}" else print "nothing" will print "nothing"

a string (including GStrings) evaluates to true if not null and not empty, false if null or empty def s = '' ... if (s) println 's is not empty' else println 's is empty' will print: 's is empty'

Collections and Maps evaluates to true if not null and not empty and false if null or empty /* an empty map example*/ def userInfo = [:] if (!userInfo) userInfo << ['user': 'Groot', 'species' : 'unknown' ] will add user: 'Groot' , species : 'unknown' as default userInfo since the u...

a null object reference evaluates to false, a non null reference to true, but for for strings, collections, iterators and enumerations it also takes into account the size. def m = null if (!m) println "empty" else println "${m}" will print "empty" de...

Sometimes it may be useful to have a specific asBoolean definition in your own program for some kind of objects. /** an oversimplified robot controller */ class RunController { def complexCondition int position = 0 def asBoolean() { return complexCondition(this...

For booleans, SQLite uses integers 0 and 1: sqlite> SELECT 2 + 2 = 4; 1 sqlite> SELECT 'a' = 'b'; 0 sqlite> SELECT typeof('a' = 'b'); integer > CREATE TABLE Users ( Name, IsAdmin ); > INSERT INTO Users VALUES ('root', 1); > INSERT INTO Users VALUES ('john', 0); > S...