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WNSupported in Synergy .NET on Windows
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YIELD MRETURN expression
or
YIELD EXIT
Arguments
expression
An expression that is evaluated and returned as a value to the enumerator object.
Discussion
The YIELD statement indicates to the compiler that the current method is an iterator block. The two versions of the YIELD syntax perform different functions:
- YIELD MRETURN expression gives the next value from the iteration (i.e., the value returned in each iteration of a FOREACH statement). It causes an element in the source sequence to be returned immediately to the caller before the next element in the sequence is accessed.
- YIELD EXIT indicates the end of iteration. Control returns to the caller of the iterator block.
Although an iterator is written as a method, the compiler translates it into a nested class that keeps track of the position of the iterator as long as the FOREACH loop on the client code continues. When YIELD MRETURN is reached, the current location is stored. Execution begins at this location the next time the iterator is called.
An iterator method must have a return type of IEnumerable or IEnumerable<> (or IAsyncEnumerable<T> if the method has both ASYNC and YIELD). A class can have multiple iterators.
A YIELD MRETURN statement cannot appear in a CATCH block, a TRY block that contains a CATCH, or a FINALLY block.
Examples
The example below returns powers of 2 using the YIELD statement.
import System.Collections
namespace ns1
public class PowersOf2
public static method Power, @IEnumerable
number, int
exponent, int
proc
data counter, int, 0
data result, int, 1
while (counter < exponent)
begin
incr counter
result = result * number
yield mreturn result
end
endmethod
endclass
endnamespace
main
proc
data i, int
foreach i in ns1.PowersOf2.Power(2,8)
begin
Console.Write(i)
Console.Write(" ")
end
Console.WriteLine()
