Return statements

A "return" statement in a function F terminates the execution of F, and optionally provides one or more result values. Any functions deferred by F are executed before F returns to its caller.

ReturnStmt = "return" [ ExpressionList ] .

In a function without a result type, a "return" statement must not specify any result values.

func noResult() {
    return
}

There are three ways to return values from a function with a result type:

1. The return value or values may be explicitly listed in the "return" statement. Each expression must be single-valued and assignable to the corresponding element of the function's result type.

   func simpleF() int {
   return 2
   }
    
   func complexF1() (re float64, im float64) {
   return -7.0, -4.0
   }
   

2. The expression list in the "return" statement may be a single call to a multi-valued function. The effect is as if each value returned from that function were assigned to a temporary variable with the type of the respective value, followed by a "return" statement listing these variables, at which point the rules of the previous case apply.

   func complexF2() (re float64, im float64) {
   return complexF1()
   }
   

3. The expression list may be empty if the function's result type specifies names for its result parameters. The result parameters act as ordinary local variables and the function may assign values to them as necessary. The "return" statement returns the values of these variables.

   func complexF3() (re float64, im float64) {
   re = 7.0
   im = 4.0
   return
   }
    
   func (devnull) Write(p []byte) (n int, _ error) {
   n = len(p)
   return
   }
   

Regardless of how they are declared, all the result values are initialized to the zero values for their type upon entry to the function. A "return" statement that specifies results sets the result parameters before any deferred functions are executed.

Implementation restriction: A compiler may disallow an empty expression list in a "return" statement if a different entity (constant, type, or variable) with the same name as a result parameter is in scope at the place of the return.

func f(n int) (res int, err error) {
    if _, err := f(n-1); err != nil {
        return  // invalid return statement: err is shadowed
    }
    return
}