How Does Go's `defer` Keyword Simplify Resource Management and Panic Handling?

Use of defer in Go

The defer keyword in Go allows you to execute a function just before the surrounding function returns, ensuring actions are taken even in the event of a panic.

Benefits of defer Over Code Placed at Function End

• Reliable Resource De-/Allocation:
  defer ensures resource cleanup, such as file closures, even when the function panics or returns abruptly.
• Panic Handling:
  Deferred functions can handle panics by calling recover(). This allows for custom error handling and recovery.
• Controlled Execution Order:
  Deferred calls are stacked in reverse order and executed upon the surrounding function's return, providing a deterministic way to deallocate resources.
• No Nested Scopes:
  Unlike try-catch-finally blocks, defer simplifies the surrounding function's structure by avoiding nested scopes.

Examples:

• Try-finally Resource Cleanup:

  func main() {
      f, err := os.Create("file")
      if err != nil {
          panic("cannot create file")
      }
      defer f.Close()
      fmt.Fprintf(f, "hello")
  }

• Try-catch-finally with Panic Handling:

  func main() {
      defer func() {
          msg := recover()
          fmt.Println(msg)
      }()
      f, err := os.Create(".") // . is the current directory
      if err != nil {
          panic("cannot create file")
      }
      defer f.Close()
      fmt.Fprintf(f, "hello")
  }

• Modified Return Values:

  func yes() (text string) {
      defer func() {
          text = "no"
      }()
      return "yes"
  }
  
  func main() {
      fmt.Println(yes()) // Prints "no"
  }

In summary, defer in Go provides a flexible way to ensure resource cleanup, handle panics, and control execution order without the need for nested block structures.

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