Changes between Initial Version and Version 1 of Yield

Timestamp:

03/23/10 11:56:14 (15 years ago)

Author:

hopscc

Comment:

--

Yield

@@ +1 @@
+= Yield =
+
+The '''yield'''  keyword signals to the compiler that the method in which it 
+appears is an iterator block. [[BR]]
+A new class is created and compiled to implement the behavior that is 
+expressed in the iterator block (implementing an IEnumerable).
+
+Within the iterator block, the yield keyword is used to provide a value to 
+the enumerator object.[[BR]] 
+This is the value that is returned, for example, in each loop of a 
+for statement. 
+
+In a '''yield''' statement, the expression is evaluated and returned as 
+a value to the enumerator object;  expression has to be implicitly 
+convertible to the yield type of the iterator.
+
+In a '''yield break''' statement, control is unconditionally returned to the 
+caller of the iterator and signals the end of iteration. 
+
+
+The yield statement can only appear inside an iterator block, 
+which can be implemented as the body of a method, operator, or accessor. 
+
+ * A '''yield''' statement cannot be located anywhere inside a try-catch block. 
+   It can be located in a try block if the try block is followed by a 
+   finally block.
+ * A '''yield break''' statement may be located in a try block or a 
+   catch block but not a finally block.
+
+== Grammar ==
+{{{
+yield [EXPRESSION]
+
+yield break
+}}}
+== Example ==
+{{{
+use System.Collections
+
+class Pwr
+    def power(num as int, exponent as int) as IEnumerable is shared
+        counter = 0
+        result  = 1
+        while counter < exponent
+            counter += 1
+            result = result * num
+            yield result
+       yield break    
+
+    def main is shared
+        # Display powers of 2 up to the exponent 8:
+        for i in .power(2, 8)
+            print i
+/#
+Output:
+2 4 8 16 32 64 128 256 
+#/
+}}}