change codes bool value to struct{} (#1270)

Closes #1269

## Fixes Or Enhances


**Make sure that you've checked the boxes below before you submit PR:**
- [ ] Tests exist or have been written that cover this particular
change.

@go-playground/validator-maintainers

Author: nar10z

baked_in.go

@@ -2769,26 +2769,26 @@ func isTimeZone(fl FieldLevel) bool {
 
 // isIso3166Alpha2 is the validation function for validating if the current field's value is a valid iso3166-1 alpha-2 country code.
 func isIso3166Alpha2(fl FieldLevel) bool {
-	val := fl.Field().String()
-	return iso3166_1_alpha2[val]
+	_, ok := iso3166_1_alpha2[fl.Field().String()]
+	return ok
 }
 
 // isIso3166Alpha2EU is the validation function for validating if the current field's value is a valid iso3166-1 alpha-2 European Union country code.
 func isIso3166Alpha2EU(fl FieldLevel) bool {
-	val := fl.Field().String()
-	return iso3166_1_alpha2_eu[val]
+	_, ok := iso3166_1_alpha2_eu[fl.Field().String()]
+	return ok
 }
 
 // isIso3166Alpha3 is the validation function for validating if the current field's value is a valid iso3166-1 alpha-3 country code.
 func isIso3166Alpha3(fl FieldLevel) bool {
-	val := fl.Field().String()
-	return iso3166_1_alpha3[val]
+	_, ok := iso3166_1_alpha3[fl.Field().String()]
+	return ok
 }
 
 // isIso3166Alpha3EU is the validation function for validating if the current field's value is a valid iso3166-1 alpha-3 European Union country code.
 func isIso3166Alpha3EU(fl FieldLevel) bool {
-	val := fl.Field().String()
-	return iso3166_1_alpha3_eu[val]
+	_, ok := iso3166_1_alpha3_eu[fl.Field().String()]
+	return ok
 }
 
 // isIso3166AlphaNumeric is the validation function for validating if the current field's value is a valid iso3166-1 alpha-numeric country code.
@@ -2810,7 +2810,9 @@ func isIso3166AlphaNumeric(fl FieldLevel) bool {
 	default:
 		panic(fmt.Sprintf("Bad field type %T", field.Interface()))
 	}
-	return iso3166_1_alpha_numeric[code]
+
+	_, ok := iso3166_1_alpha_numeric[code]
+	return ok
 }
 
 // isIso3166AlphaNumericEU is the validation function for validating if the current field's value is a valid iso3166-1 alpha-numeric European Union country code.
@@ -2832,19 +2834,21 @@ func isIso3166AlphaNumericEU(fl FieldLevel) bool {
 	default:
 		panic(fmt.Sprintf("Bad field type %T", field.Interface()))
 	}
-	return iso3166_1_alpha_numeric_eu[code]
+
+	_, ok := iso3166_1_alpha_numeric_eu[code]
+	return ok
 }
 
 // isIso31662 is the validation function for validating if the current field's value is a valid iso3166-2 code.
 func isIso31662(fl FieldLevel) bool {
-	val := fl.Field().String()
-	return iso3166_2[val]
+	_, ok := iso3166_2[fl.Field().String()]
+	return ok
 }
 
 // isIso4217 is the validation function for validating if the current field's value is a valid iso4217 currency code.
 func isIso4217(fl FieldLevel) bool {
-	val := fl.Field().String()
-	return iso4217[val]
+	_, ok := iso4217[fl.Field().String()]
+	return ok
 }
 
 // isIso4217Numeric is the validation function for validating if the current field's value is a valid iso4217 numeric currency code.
@@ -2860,7 +2864,9 @@ func isIso4217Numeric(fl FieldLevel) bool {
 	default:
 		panic(fmt.Sprintf("Bad field type %T", field.Interface()))
 	}
-	return iso4217_numeric[code]
+
+	_, ok := iso4217_numeric[code]
+	return ok
 }
 
 // isBCP47LanguageTag is the validation function for validating if the current field's value is a valid BCP 47 language tag, as parsed by language.Parse