c# - Why can't "return" and "yield return" be used in the same method? -

why can't use both return , yield return in same method?

for example, can have getintegers1 , getintegers2 below, not getintegers3.

public ienumerable<int> getintegers1() {   return new[] { 4, 5, 6 }; }  public ienumerable<int> getintegers2() {   yield return 1;   yield return 2;   yield return 3; }  public ienumerable<int> getintegers3() {   if ( somecondition )   {     return new[] {4, 5, 6}; // compiler error   }   else   {     yield return 1;     yield return 2;     yield return 3;   } } 

return eager. returns entire resultset @ once. yield return builds enumerator. behind scenes c# compiler emits necessary class enumerator when use yield return. compiler doesn't runtime conditions such if ( somecondition ) when determining whether should emit code enumerable or have method returns simple array. detects in method using both not possible cannot emit code enumerator , @ same time have method return normal array , same method.