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Published: Mar 18, 2023 License: MIT, MIT Imports: 4 Imported by: 0



The sqlx package has special reflect needs. In particular, it needs to:

  • be able to map a name to a field
  • understand embedded structs
  • understand mapping names to fields by a particular tag
  • user specified name -> field mapping functions

These behaviors mimic the behaviors by the standard library marshallers and also the behavior of standard Go accessors.

The first two are amply taken care of by Reflect.Value.FieldByName, and the third is addressed by Reflect.Value.FieldByNameFunc, but these don't quite understand struct tags in the ways that are vital to most marshalers, and they are slow.

This reflectx package extends reflect to achieve these goals.



Package reflectx implements extensions to the standard reflect lib suitable for implementing marshalling and unmarshalling packages. The main Mapper type allows for Go-compatible named attribute access, including accessing embedded struct attributes and the ability to use functions and struct tags to customize field names.



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func Deref

func Deref(t reflect.Type) reflect.Type

Deref is Indirect for reflect.Types

func FieldByIndexes

func FieldByIndexes(v reflect.Value, indexes []int) reflect.Value

FieldByIndexes returns a value for the field given by the struct traversal for the given value.

func FieldByIndexesReadOnly

func FieldByIndexesReadOnly(v reflect.Value, indexes []int) reflect.Value

FieldByIndexesReadOnly returns a value for a particular struct traversal, but is not concerned with allocating nil pointers because the value is going to be used for reading and not setting.


type FieldInfo

type FieldInfo struct {
	Index    []int
	Path     string
	Field    reflect.StructField
	Zero     reflect.Value
	Name     string
	Options  map[string]string
	Embedded bool
	Children []*FieldInfo
	Parent   *FieldInfo

A FieldInfo is metadata for a struct field.

type Mapper

type Mapper struct {
	// contains filtered or unexported fields

Mapper is a general purpose mapper of names to struct fields. A Mapper behaves like most marshallers in the standard library, obeying a field tag for name mapping but also providing a basic transform function.

func NewMapper

func NewMapper(tagName string) *Mapper

NewMapper returns a new mapper using the tagName as its struct field tag. If tagName is the empty string, it is ignored.

func NewMapperFunc

func NewMapperFunc(tagName string, f func(string) string) *Mapper

NewMapperFunc returns a new mapper which optionally obeys a field tag and a struct field name mapper func given by f. Tags will take precedence, but for any other field, the mapped name will be f(field.Name)

func NewMapperTagFunc

func NewMapperTagFunc(tagName string, mapFunc, tagMapFunc func(string) string) *Mapper

NewMapperTagFunc returns a new mapper which contains a mapper for field names AND a mapper for tag values. This is useful for tags like json which can have values like "name,omitempty".

func (*Mapper) FieldByName

func (m *Mapper) FieldByName(v reflect.Value, name string) reflect.Value

FieldByName returns a field by its mapped name as a reflect.Value. Panics if v's Kind is not Struct or v is not Indirectable to a struct Kind. Returns zero Value if the name is not found.

func (*Mapper) FieldMap

func (m *Mapper) FieldMap(v reflect.Value) map[string]reflect.Value

FieldMap returns the mapper's mapping of field names to reflect values. Panics if v's Kind is not Struct, or v is not Indirectable to a struct kind.

func (*Mapper) FieldsByName

func (m *Mapper) FieldsByName(v reflect.Value, names []string) []reflect.Value

FieldsByName returns a slice of values corresponding to the slice of names for the value. Panics if v's Kind is not Struct or v is not Indirectable to a struct Kind. Returns zero Value for each name not found.

func (*Mapper) TraversalsByName

func (m *Mapper) TraversalsByName(t reflect.Type, names []string) [][]int

TraversalsByName returns a slice of int slices which represent the struct traversals for each mapped name. Panics if t is not a struct or Indirectable to a struct. Returns empty int slice for each name not found.

func (*Mapper) TraversalsByNameFunc

func (m *Mapper) TraversalsByNameFunc(t reflect.Type, names []string, fn func(int, []int) error) error

TraversalsByNameFunc traverses the mapped names and calls fn with the index of each name and the struct traversal represented by that name. Panics if t is not a struct or Indirectable to a struct. Returns the first error returned by fn or nil.

func (*Mapper) TypeMap

func (m *Mapper) TypeMap(t reflect.Type) *StructMap

TypeMap returns a mapping of field strings to int slices representing the traversal down the struct to reach the field.

type StructMap

type StructMap struct {
	Tree  *FieldInfo
	Index []*FieldInfo
	Paths map[string]*FieldInfo
	Names map[string]*FieldInfo

A StructMap is an index of field metadata for a struct.

func (StructMap) GetByPath

func (f StructMap) GetByPath(path string) *FieldInfo

GetByPath returns a *FieldInfo for a given string path.

func (StructMap) GetByTraversal

func (f StructMap) GetByTraversal(index []int) *FieldInfo

GetByTraversal returns a *FieldInfo for a given integer path. It is analogous to reflect.FieldByIndex, but using the cached traversal rather than re-executing the reflect machinery each time.

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