Nested function calls in a defer statement.

nested_defer.go

package main

import "log"

func foo1(n int) int {
	log.Println("foo1", n)
	return n
}
func foo2(n int) int {
	log.Println("foo2", n)
	return n
}
func foo3(n int) int {
	log.Println("foo3", n)
	return n
}

func deferOneFunctionCall() {
	defer foo1(foo2(foo3(1)))
	log.Println("defer-----")
}

func deferThreeFunctionCalls() {
	defer func() { foo1(foo2(foo3(1))) }()
	log.Println("defer-----")
}

// Nested function calls in a defer statement.
//
// A defer statement defers only a single function.
// This means any function call evaluating an argument to a deferred function is not deferred.
// Each time a defer statement executes, the function value and parameters to the call are evaluated as usual.
func main() {
	log.Println("deferOneFunctionCall()")
	deferOneFunctionCall()
	log.Println()
	log.Println("deferThreeFunctionCalls()")
	deferThreeFunctionCalls()
}
// 2019/12/06 17:23:56 deferOneFunctionCall()
// 2019/12/06 17:23:56 foo3 1
// 2019/12/06 17:23:56 foo2 1
// 2019/12/06 17:23:56 defer-----
// 2019/12/06 17:23:56 foo1 1
// 2019/12/06 17:23:56
// 2019/12/06 17:23:56 deferThreeFunctionCalls()
// 2019/12/06 17:23:56 defer-----
// 2019/12/06 17:23:56 foo3 1
// 2019/12/06 17:23:56 foo2 1
// 2019/12/06 17:23:56 foo1 1