How to Safely Delete Elements from an Array of Structs in Go Loops?

Deleting Elements from an Array of Structs in Go Loops

When working with arrays of structs, it is often necessary to delete elements based on a specific condition. However, implementing this deletion logic can be tricky and can lead to errors. This article will explore the best practices for deleting elements from an array of structs in a Go loop.

Consider the following array of structs:

type Config struct {
  Applications []Application
}

config := new(Config)
_ = decoder.Decode(&config)

Now, within the loop, you may encounter a scenario where you need to delete an element from config.Applications based on a key.

for i, application := range config.Applications {
  if i == 1 {
    config.Applications = _removeApplication(i, config.Applications)
  }
}

func _removeApplication(i int, list []Application) []Application {
  if i < len(list)-1 {
    list = append(list[:i], list[i+1:]...)
  } else {
    log.Print(list[i].Name)
    list = list[:i]
  }

  return list
}

Unfortunately, this code may result in an "out of range" error. To resolve this, we can leverage the following techniques:

Delete from the End to the Beginning:

As per the Slice Tricks page, one can delete an element at index i as follows:

a = append(a[:i], a[i+1:]...)

This approach ensures that all subsequent elements are shifted left after the deletion, without affecting the current loop index. However, it's worth noting that iterating over a slice while deleting requires caution, as it can lead to unpredictable results.

Use a Downward Loop:

To avoid these issues, you can utilize a downward loop that starts from the last element of the slice. This way, deleting an element does not affect any previous elements in the loop:

for i := len(config.Applications) - 1; i >= 0; i-- {
    application := config.Applications[i]
    // Condition to decide if the current element has to be deleted:
    if haveToDelete {
        config.Applications = append(config.Applications[:i],
                config.Applications[i+1:]...)
    }
}

By following these best practices, you can effectively and safely remove elements from an array of structs in Go loops.

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