Unfamiliar yield keywords

What is the function of the yield keyword? It is estimated that most people are confused like me before. I pay attention to him after preparing an interview question.

I checked Msdn's description about yield: In the iterator block, it is used to provide a value to the enumerated number object or send an iteration end signal.

It's still a fog. Let me take a look at it. yield appears in the loop body and returns the current operation result in each loop. yield is used with return or break to act as a flag of method output.

The difference between yield return and return:

 

For example:

 

Int n = 1;

Int m = 100;

While (n <100)

{

N + = n;

Yield return n; // result 2, 4, 8 ,......

}

 

Return indicates that the entire method is terminated and the current result is returned.

Yield return is an introduction to the current loop. It returns the current result and starts the next loop.

 

The Return Value of the method using the yield keyword is generally IEnumerable.

The execution process of the sample Msdn yield code.

In the following example, the yield statement is used in the iterator block (the method Power (int number, int power. When the Power method is called, it returns an enumerative object containing the number Power. Note that the return type of the Power method is IEnumerable (an iterator interface type ).

 

Using System;
Using System. Collections;
Public class List
{
Public static IEnumerable Power (int number, int exponent)
{
Int counter = 0;
Int result = 1; // <--------------- (2)
While (counter ++ <exponent) // <--------------- (3)
{
Result = result * number;
Yield return result;
}
}

Static void Main ()
{
// Display powers of 2 up to the exponent 8:
Foreach (int I in Power (2, 8) // <----------------- (1)
{
Console. Write ("{0}", I); // <--------------- (4)
}
}
}

 

Returned results: 2 4 8 16 32 64 128 256.

 

First, the program runs to (1), jumps to the Power method, runs to (2), enters (3) for the first time, returns the result to (4) output, (1) starts from (3) and returns result (4.