Method Lookup

Reflection can check whether a type exposes a named method.

methods Use method lookup for inspection and adapters, but keep normal code paths explicit when possible.

methodName methodName = "Summary" (default)methodName = "Missing"

method_lookup.go

Replay: real traced execution (multi-file project)

package main

import (
	"fmt"
	"reflect"
)

type Report struct {
	Title string
}

func (r Report) Summary() string {
	return "report:" + r.Title
}

func main() {
	var methodName = "Summary"
	reportType := reflect.TypeOf(Report{})
	method, ok := reportType.MethodByName(methodName)
	methodType := "none"
	if ok {
		methodType = method.Type.String()
	}

	fmt.Println("method_name=", methodName)
	fmt.Println("found=", ok)
	fmt.Println("method_count=", reportType.NumMethod())
	fmt.Println("method_type=", methodType)
}

package main

import (
	"fmt"
	"reflect"
)

type Report struct {
	Title string
}

func (r Report) Summary() string {
	return "report:" + r.Title
}

func main() {
	var methodName = "Missing"
	reportType := reflect.TypeOf(Report{})
	method, ok := reportType.MethodByName(methodName)
	methodType := "none"
	if ok {
		methodType = method.Type.String()
	}

	fmt.Println("method_name=", methodName)
	fmt.Println("found=", ok)
	fmt.Println("method_count=", reportType.NumMethod())
	fmt.Println("method_type=", methodType)
}

methodName ← "Summary", reportType ← &reflect.rtype{t:abi.Type{Size_:0x10, PtrBytes:0x8, Hash:⟨addr A⟩, TFlag:0x7, Align_:0x8, FieldAlign_:0x8, Kind_:0x19, Equal:(func(unsafe.Pointer, unsafe.Pointer) bool)(⟨addr B⟩), GCData:(*uint8)(⟨addr C⟩), Str:10681, PtrToThis:64032}}

⋯16func main() {17  var methodName→ "Summary" = "Summary" //@methodName="Missing"18  reportType→ &reflect.rtype{t:abi.Type{Size_:0x10, PtrBytes:0x8, Hash:⟨addr A⟩, TFlag:0x7, Align_:0x8, FieldAlign_:0x8, Kind_:0x19, Equal:(func(unsafe.Pointer, unsafe.Pointer) bool)(⟨addr B⟩), GCData:(*uint8)(⟨addr C⟩), Str:10681, PtrToThis:64032}} := reflect.TypeOf(Report{})19  method→ reflect.Method{Name:"Summary", PkgPath:"", Type:(*reflect.rtype)(⟨addr D⟩), Func:reflect.Value{typ_:(*abi.Type)(⟨addr D⟩), ptr:(unsafe.Pointer)(⟨addr E⟩), flag:0x13}, Index:0}, ok→ true := reportType&reflect.rtype{t:abi.Type{Size_:0x10, PtrBytes:0x8, Hash:⟨addr A⟩, TFlag:0x7, Align_:0x8, FieldAlign_:0x8, Kind_:0x19, Equal:(func(unsafe.Pointer, unsafe.Pointer) bool)(⟨addr B⟩), GCData:(*uint8)(⟨addr C⟩), Str:10681, PtrToThis:64032}}.MethodByName(methodName"Summary")20  methodType→ "none" := "none"21  if ok {⋯

methodType ← "func(main.Report) string"

⋯20methodType := "none"21if oktrue {22  methodType→ "func(main.Report) string" = method.Type&reflect.rtype{t:abi.Type{Size_:0x8, PtrBytes:0x8, Hash:⟨addr F⟩, TFlag:0x0, Align_:0x8, FieldAlign_:0x8, Kind_:0x33, Equal:(func(unsafe.Pointer, unsafe.Pointer) bool)(nil), GCData:(*uint8)(⟨addr C⟩), Str:-8, PtrToThis:0}}.String()23}⋯

fmt.Println("method_name=", methodName)

⋯25  fmt.Println("method_name=", methodName"Summary")26  fmt.Println("found=", oktrue)27  fmt.Println("method_count=", reportType&reflect.rtype{t:abi.Type{Size_:0x10, PtrBytes:0x8, Hash:⟨addr A⟩, TFlag:0x7, Align_:0x8, FieldAlign_:0x8, Kind_:0x19, Equal:(func(unsafe.Pointer, unsafe.Pointer) bool)(⟨addr B⟩), GCData:(*uint8)(⟨addr C⟩), Str:10681, PtrToThis:64032}}.NumMethod())28  fmt.Println("method_type=", methodType"func(main.Report) string")29}⋯

outputmethod_name= Summary
found= true
method_count= 1
method_type= func(main.Report) string

methodName ← "Missing", reportType ← &reflect.rtype{t:abi.Type{Size_:0x10, PtrBytes:0x8, Hash:⟨addr A⟩, TFlag:0x7, Align_:0x8, FieldAlign_:0x8, Kind_:0x19, Equal:(func(unsafe.Pointer, unsafe.Pointer) bool)(⟨addr B⟩), GCData:(*uint8)(⟨addr C⟩), Str:10681, PtrToThis:64032}}

⋯16func main() {17  var methodName→ "Missing" = "Missing"18  reportType→ &reflect.rtype{t:abi.Type{Size_:0x10, PtrBytes:0x8, Hash:⟨addr A⟩, TFlag:0x7, Align_:0x8, FieldAlign_:0x8, Kind_:0x19, Equal:(func(unsafe.Pointer, unsafe.Pointer) bool)(⟨addr B⟩), GCData:(*uint8)(⟨addr C⟩), Str:10681, PtrToThis:64032}} := reflect.TypeOf(Report{})19  method→ reflect.Method{Name:"", PkgPath:"", Type:reflect.Type(nil), Func:reflect.Value{typ_:(*abi.Type)(nil), ptr:(unsafe.Pointer)(nil), flag:0x0}, Index:0}, ok→ false := reportType&reflect.rtype{t:abi.Type{Size_:0x10, PtrBytes:0x8, Hash:⟨addr A⟩, TFlag:0x7, Align_:0x8, FieldAlign_:0x8, Kind_:0x19, Equal:(func(unsafe.Pointer, unsafe.Pointer) bool)(⟨addr B⟩), GCData:(*uint8)(⟨addr C⟩), Str:10681, PtrToThis:64032}}.MethodByName(methodName"Missing")20  methodType→ "none" := "none"21  if ok {22    methodType = method.Type.String()23  }2425  fmt.Println("method_name=", methodName"Missing")26  fmt.Println("found=", okfalse)27  fmt.Println("method_count=", reportType&reflect.rtype{t:abi.Type{Size_:0x10, PtrBytes:0x8, Hash:⟨addr A⟩, TFlag:0x7, Align_:0x8, FieldAlign_:0x8, Kind_:0x19, Equal:(func(unsafe.Pointer, unsafe.Pointer) bool)(⟨addr B⟩), GCData:(*uint8)(⟨addr C⟩), Str:10681, PtrToThis:64032}}.NumMethod())28  fmt.Println("method_type=", methodType"none")29}⋯

outputmethod_name= Missing
found= false
method_count= 1
method_type= none