88 lines
2.6 KiB
Go
88 lines
2.6 KiB
Go
// Package options provides a way to pass unstructured sets of options to a
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// component expecting a strongly-typed configuration structure.
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package options
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import (
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"fmt"
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"reflect"
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)
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// NoSuchFieldError is the error returned when the generic parameters hold a
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// value for a field absent from the destination structure.
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type NoSuchFieldError struct {
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Field string
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Type string
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}
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func (e NoSuchFieldError) Error() string {
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return fmt.Sprintf("no field %q in type %q", e.Field, e.Type)
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}
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// CannotSetFieldError is the error returned when the generic parameters hold a
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// value for a field that cannot be set in the destination structure.
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type CannotSetFieldError struct {
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Field string
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Type string
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}
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func (e CannotSetFieldError) Error() string {
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return fmt.Sprintf("cannot set field %q of type %q", e.Field, e.Type)
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}
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// TypeMismatchError is the error returned when the type of the generic value
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// for a field mismatches the type of the destination structure.
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type TypeMismatchError struct {
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Field string
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ExpectType string
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ActualType string
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}
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func (e TypeMismatchError) Error() string {
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return fmt.Sprintf("type mismatch, field %s require type %v, actual type %v", e.Field, e.ExpectType, e.ActualType)
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}
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// Generic is a basic type to store arbitrary settings.
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type Generic map[string]interface{}
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// NewGeneric returns a new Generic instance.
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func NewGeneric() Generic {
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return make(Generic)
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}
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// GenerateFromModel takes the generic options, and tries to build a new
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// instance of the model's type by matching keys from the generic options to
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// fields in the model.
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//
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// The return value is of the same type than the model (including a potential
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// pointer qualifier).
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func GenerateFromModel(options Generic, model interface{}) (interface{}, error) {
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modType := reflect.TypeOf(model)
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// If the model is of pointer type, we need to dereference for New.
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resType := reflect.TypeOf(model)
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if modType.Kind() == reflect.Ptr {
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resType = resType.Elem()
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}
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// Populate the result structure with the generic layout content.
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res := reflect.New(resType)
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for name, value := range options {
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field := res.Elem().FieldByName(name)
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if !field.IsValid() {
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return nil, NoSuchFieldError{name, resType.String()}
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}
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if !field.CanSet() {
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return nil, CannotSetFieldError{name, resType.String()}
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}
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if reflect.TypeOf(value) != field.Type() {
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return nil, TypeMismatchError{name, field.Type().String(), reflect.TypeOf(value).String()}
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}
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field.Set(reflect.ValueOf(value))
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}
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// If the model is not of pointer type, return content of the result.
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if modType.Kind() == reflect.Ptr {
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return res.Interface(), nil
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}
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return res.Elem().Interface(), nil
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}
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