Changes between Initial Version and Version 1 of ConditionalExpr

Timestamp:

12/22/09 13:38:18 (15 years ago)

Author:

hopscc

Comment:

--

ConditionalExpr

@@ +1 @@
+= Conditional Expressions =
+
+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.
+
+nillable objects (e.g nillable boolean, nillable int) test true if both non nil and non nil object is 'true' (non false or non zero)
+
+== Examples ==
+
+{{{
+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'
+
+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
+ 
+}}}
+