refl

README

Go reflection helpers

This library provides helper functions to work with structures and field tags.

Documentation

Overview

Package refl provides reflection helpers.

Index

• Constants
• func As(v interface{}, target interface{}) bool
• func DeepIndirect(t reflect.Type) reflect.Type
• func FindEmbeddedSliceOrMap(i interface{}) reflect.Type
• func FindTaggedName(structPtr, fieldPtr interface{}, tagName string) (string, error)
• func HasTaggedFields(i interface{}, tagName string) bool
• func IsScalar(i interface{}) bool
• func IsSliceOrMap(i interface{}) bool
• func IsStruct(i interface{}) bool
• func IsZero(v reflect.Value) bool
• func JoinErrors(errs ...error) error
• func NoEmptyFields(l interface{}) error
• func PopulateFieldsFromTags(structPtr interface{}, fieldTag reflect.StructTag) error
• func ReadBoolPtrTag(tag reflect.StructTag, name string, holder **bool) error
• func ReadBoolTag(tag reflect.StructTag, name string, holder *bool) error
• func ReadFloatPtrTag(tag reflect.StructTag, name string, holder **float64) error
• func ReadFloatTag(tag reflect.StructTag, name string, holder *float64) error
• func ReadIntPtrTag(tag reflect.StructTag, name string, holder **int64) error
• func ReadIntTag(tag reflect.StructTag, name string, holder *int64) error
• func ReadStringPtrTag(tag reflect.StructTag, name string, holder **string)
• func ReadStringTag(tag reflect.StructTag, name string, holder *string)
• func Tagged(structPtr, fieldPtr interface{}, tagName string) string
• func WalkFieldsRecursively(v reflect.Value, f WalkFieldFn)
• func WalkTaggedFields(v reflect.Value, f WalkTaggedFieldFn, tagName string)
• type SentinelError
  • func (se SentinelError) Error() string
• type TypeString
  • func GoType(t reflect.Type) TypeString
• type WalkFieldFn
• type WalkTaggedFieldFn

Examples

• As
• GoType
• PopulateFieldsFromTags

Constants

const (
	ErrNeedPointer          = SentinelError("could not find field value in struct")
	ErrMissingFieldValue    = SentinelError("can not take address of structure, please pass a pointer")
	ErrMissingStructOrField = SentinelError("structPtr and fieldPtr are required")
	ErrEmptyFields          = SentinelError("empty fields")
	ErrStructExpected       = SentinelError("struct expected")
)

Sentinel errors.

Functions

func As

func As(v interface{}, target interface{}) bool

As unwraps interface value to find value assignable to target.

Example

package main

import (
	"encoding/json"
	"fmt"

	"github.com/swaggest/refl"
)

func main() {
	var (
		v  interface{}
		vv json.Marshaler
	)

	vv = json.RawMessage(`{"abc":123}`)
	v = vv

	target := new(json.RawMessage)
	fmt.Println(refl.As(v, target), string(*target))

}

Output:

true {"abc":123}

func DeepIndirect

func DeepIndirect(t reflect.Type) reflect.Type

DeepIndirect returns first encountered non-pointer type.

func FindEmbeddedSliceOrMap

func FindEmbeddedSliceOrMap(i interface{}) reflect.Type

FindEmbeddedSliceOrMap checks if variable has a slice/array/map or a pointer to it embedded.

func FindTaggedName

func FindTaggedName(structPtr, fieldPtr interface{}, tagName string) (string, error)

FindTaggedName returns tagged name of an entity field.

Entity field is defined by pointer to owner structure and pointer to field in that structure.

entity := MyEntity{}
name, found := sm.FindTaggedName(&entity, &entity.UpdatedAt, "db")

func HasTaggedFields

func HasTaggedFields(i interface{}, tagName string) bool

HasTaggedFields checks if the structure has fields with tag name.

func IsScalar

func IsScalar(i interface{}) bool

IsScalar checks if variable is an integer, float, complex, bool, string or a pointer to it.

func IsSliceOrMap

func IsSliceOrMap(i interface{}) bool

IsSliceOrMap checks if variable is a slice/array/map or a pointer to it.

func IsStruct

func IsStruct(i interface{}) bool

IsStruct checks if variable is a struct or a pointer to a struct.

func IsZero

func IsZero(v reflect.Value) bool

IsZero reports whether v is the zero value for its type. It panics if the argument is invalid.

Adapted from go1.13 reflect.IsZero.

func JoinErrors

func JoinErrors(errs ...error) error

JoinErrors joins non-nil errors.

func NoEmptyFields

func NoEmptyFields(l interface{}) error

NoEmptyFields checks structure (or a pointer to it) for potentially uninitialized fields. Fields with zero values are considered uninitialized.

func PopulateFieldsFromTags

func PopulateFieldsFromTags(structPtr interface{}, fieldTag reflect.StructTag) error

PopulateFieldsFromTags extracts values from field tag and puts them in according property of structPtr.

Example

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"reflect"

	"github.com/swaggest/refl"
)

func main() {
	type schema struct {
		Title      string
		Desc       *string
		Min        *float64
		Max        float64
		Limit      int64
		Offset     *int64
		Deprecated bool
		Required   *bool
	}

	type value struct {
		Property string `title:"Value" desc:"..." min:"-1.23" max:"10.1" limit:"5" offset:"2" deprecated:"true" required:"f"`
	}

	s := schema{}
	tag := reflect.TypeOf(value{}).Field(0).Tag

	err := refl.PopulateFieldsFromTags(&s, tag)
	if err != nil {
		log.Fatal(err)
	}

	j, err := json.Marshal(s)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(string(j))

}

Output:

{"Title":"Value","Desc":"...","Min":-1.23,"Max":10.1,"Limit":5,"Offset":2,"Deprecated":true,"Required":false}

func ReadBoolPtrTag

func ReadBoolPtrTag(tag reflect.StructTag, name string, holder **bool) error

ReadBoolPtrTag reads bool value from field tag into a pointer.

func ReadBoolTag

func ReadBoolTag(tag reflect.StructTag, name string, holder *bool) error

ReadBoolTag reads bool value from field tag into a value.

func ReadFloatPtrTag

func ReadFloatPtrTag(tag reflect.StructTag, name string, holder **float64) error

ReadFloatPtrTag reads float64 value from field tag into a pointer.

func ReadFloatTag

func ReadFloatTag(tag reflect.StructTag, name string, holder *float64) error

ReadFloatTag reads float64 value from field tag into a value.

func ReadIntPtrTag

func ReadIntPtrTag(tag reflect.StructTag, name string, holder **int64) error

ReadIntPtrTag reads int64 value from field tag into a pointer.

func ReadIntTag

func ReadIntTag(tag reflect.StructTag, name string, holder *int64) error

ReadIntTag reads int64 value from field tag into a value.

func ReadStringPtrTag

func ReadStringPtrTag(tag reflect.StructTag, name string, holder **string)

ReadStringPtrTag reads string value from field tag into a pointer.

func ReadStringTag

func ReadStringTag(tag reflect.StructTag, name string, holder *string)

ReadStringTag reads string value from field tag into a value.

func Tagged

func Tagged(structPtr, fieldPtr interface{}, tagName string) string

Tagged will try to find tagged name and panic on error.

func WalkFieldsRecursively

func WalkFieldsRecursively(v reflect.Value, f WalkFieldFn)

WalkFieldsRecursively walks scalar and non-scalar fields of a struct recursively and calls user function on them.

func WalkTaggedFields

func WalkTaggedFields(v reflect.Value, f WalkTaggedFieldFn, tagName string)

WalkTaggedFields iterates top level fields of structure including anonymous embedded fields. If tagName is empty function is called for all top level fields.

Types

type SentinelError

type SentinelError string

SentinelError is a constant error.

func (SentinelError) Error

func (se SentinelError) Error() string

Error implements error.

type TypeString

type TypeString string

TypeString is a type name with import path.

func GoType

func GoType(t reflect.Type) TypeString

GoType returns string representation of type name including import path.

Example

package main

import (
	"fmt"
	"reflect"

	"github.com/swaggest/refl"
	fancypath "github.com/swaggest/refl/internal/Fancy-Path"
	"github.com/swaggest/refl/internal/sample"
)

func main() {
	fmt.Println(refl.GoType(reflect.TypeOf(new(fancypath.Sample))))
	fmt.Println(refl.GoType(reflect.TypeOf(new(sample.TestSampleStruct))))

}

Output:

*github.com/swaggest/refl/internal/Fancy-Path::fancypath.Sample
*github.com/swaggest/refl/internal/sample.TestSampleStruct

type WalkFieldFn

type WalkFieldFn func(v reflect.Value, sf reflect.StructField, path []reflect.StructField)

WalkFieldFn defines callback.

type WalkTaggedFieldFn

type WalkTaggedFieldFn func(v reflect.Value, sf reflect.StructField, tag string)

WalkTaggedFieldFn defines callback.