A conditional expression is an expression that produces a value that can be (conveniently) construed as a boolean
true or false value.
These are used directly in if and while flow control statements and the assert statement
Any of following can be used as conditional expressions and produce a boolean true value.
- non false (bool Type - expression or variable )
- numeric not 0
- non zero char
- not nil
- blank strings and empty collections are true (non nil) - must check .length for strings and .count for collections for checking non empty.
nilable types (e.g nilable boolean, nilable int) test true if both non nil and the non nil object is 'true' (non false or non zero)
A nilable Object and nilable String (Object?, String? ) tests true if the instance is non-nil (no subsequent truth test beyond that)
a = 100 gt20 = a > 20 if a # numeric non zero print 'a non zero' if a > 10 # boolean condition print 'greater than 10' assert gt20 # boolean variable - succeeds true assert a > 20 # boolean condition same as above ch = c'x' if ch print 'ch non zero' assert ch ch=c'\0' if not ch # negated condition print 'ch is zero' s as String? # nillable string unset value if s print 's not nil' if s.length print 's not empty' else print 's is nil' assert s # succeeds if s is not nil s1 as String ='...' # non-nilable string with or without (0 length) value if s.length print 's not empty' else print 's is length 0' assert s1 # always succeeds - non nilable (warning) assert s1.length # succeeds if s1 is not empty ( > length 0) l =  # empty list assert l # succeeds not nil assert l.count # fails empty list ln as List?<of dynamic> # nillable list - unset assert ln # fails: ln not set so nil nb = a>10 to ? # bool expr cast to nillable bool assert nb # succeeds non nil and true nb = a<5 assert nb # fails a is >5 so variable is false nb = nil assert nb # also fails variable is nil #nilable Object shouldBeFalse as Object? = false # bool value typed as nilable Anything assert shouldBeFalse == false # ok shouldBeTrue0 = not shouldBeFalse # tests against nil only assert shouldBeTrue0 == true # fails assertion shouldBeTrue = not (shouldBeFalse to bool) assert shouldBeTrue == true # ok