github.com/facebookincubator/go-belt@v0.0.0-20230703220935-39cd348f1a38/pkg/field/abstract_fields.go

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package field

// ForEachFieldser is an iterator through a collection of fields.
//
// Any object which implements this interface may be used as a source
// of fields. For example a generic parser of field values in a Logger
// checks if a value implements this interface, and if does, then
// it is used to provide the fields instead of using a generic method.
type ForEachFieldser interface {
	// ForEachField iterates through all the fields, until first false is returned.
	//
	// WARNING! This callback is supposed to be used only to read
	// the field content, but not to hold the pointer to the field itself.
	// For the purposes of performance optimizations it is assumed
	// that the pointer is not escapable. If it is required to store
	// the pointer to the field after `callback` returned then copy the field.
	// Otherwise Go's memory guarantees are broken.
	ForEachField(callback func(f *Field) bool) bool
}

// AbstractFields is an abstraction of any types of collections of fields.
type AbstractFields interface {
	ForEachFieldser
	Len() int
}

// Slice is a collection of collections of fields.
type Slice[T AbstractFields] []T

// Len implements AbstractFields.
func (s Slice[T]) Len() int {
	count := 0
	for _, items := range s {
		count += items.Len()
	}
	return count
}

// ForEachField implements AbstractFields.
func (s Slice[T]) ForEachField(callback func(f *Field) bool) bool {
	for _, items := range s {
		if !items.ForEachField(callback) {
			return false
		}
	}
	return true
}

// Slicer implements AbstractFields providing a subset of fields (reported through
// method ForEachField of the initial collection).
type Slicer[T AbstractFields] struct {
	All      T
	StartIdx uint
	EndIdx   uint
}

var _ AbstractFields = (*Slicer[AbstractFields])(nil)

// Len implements AbstractFields.
func (s *Slicer[T]) Len() int {
	count := 0
	s.ForEachField(func(f *Field) bool {
		count++
		return true
	})
	return count
}

// ForEachField implements AbstractFields.
func (s *Slicer[T]) ForEachField(callback func(f *Field) bool) bool {
	idx := uint(0)
	return s.All.ForEachField(func(f *Field) bool {
		if idx >= s.EndIdx {
			return false
		}
		if idx >= s.StartIdx {
			if !callback(f) {
				return false
			}
		}
		idx++
		return true
	})
}

// NewSlicer provides a subset of fields (reported through method ForEachField of the initial collection).
func NewSlicer[T AbstractFields](all T, startIdx, endIdx uint) *Slicer[T] {
	return &Slicer[T]{
		All:      all,
		StartIdx: startIdx,
		EndIdx:   endIdx,
	}
}

// Gather copies all the fields into a slice and returns it.
func Gather[T AbstractFields](fields T) Fields {
	result := make(Fields, 0, fields.Len())
	fields.ForEachField(func(field *Field) bool {
		result = append(result, *field)
		return true
	})
	return result
}