question about overload condition operator == #818

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1. seruman commented on Aug 7, 2025

   

   seruman

   on Aug 7, 2025

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   You need to have status in your environment to reference it in the expression;

   type FilterEnv struct {
   +   Status    json.Number `expr:"status"`
       JsonNumEq func(a json.Number, b any) bool
   }

   See; https://go.dev/play/p/gKd6LxdiVLN
   Second example here with a struct environment might be useful; https://expr-lang.org/#examples
2. ForeverCzz commented on Aug 8, 2025

   

   ForeverCzz

   on Aug 8, 2025

   Author

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   I need to process dynamic fields by using map in project.
   And because of that, Vistor-Patch seems more compatible to my code.

   type jsonNumEqPatch struct{}
   
   func (jsonNumEqPatch) Visit(node *ast.Node) {
   	if n, ok := (*node).(*ast.BinaryNode); ok && n.Operator == "==" {
   		callNode := &ast.CallNode{
   			Callee:    &ast.IdentifierNode{Value: "jsonNumEq"},
   			Arguments: []ast.Node{n.Left, n.Right},
   		}
   		ast.Patch(node, callNode)
   
   		(*node).SetType(reflect.TypeOf(true)) // set return value type
   	}
   }
   
   var customFilterFunc = []expr.Option{
   	// jsonNumEq overloads operator ==
   	expr.Function(
   		"jsonNumEq",
   		func(params ...any) (any, error) {
   			return fmt.Sprint(params[0]) == fmt.Sprint(params[1]), nil
   		}),
   }
   
   // Filter api
   type Filter interface {
   	Run(map[string]any) (bool, error)
   }
   
   type exprFilter struct {
   	p *vm.Program
   }
   
   // NewFilter builds a expr filter
   func NewFilter(config string) (Filter, error) {
   	f := exprFilter{}
   	if config == "" {
   		return f, nil
   	}
   	opts := []expr.Option{expr.Patch(jsonNumEqPatch{})}
   	opts = append(opts, customFilterFunc...)
   
   	p, err := expr.Compile(config, opts...)
   	if err != nil {
   		return f, err
   	}
   	f.p = p
   	return f, nil
   }
   
   // Run runs the expr expression in exprFilter. It returns true if input passes the filter.
   func (f exprFilter) Run(input map[string]any) (bool, error) {
   	if f.p == nil {
   		return true, nil
   	}
   	v, err := expr.Run(f.p, input)
   	if err != nil {
   		return false, err
   	}
   	res, ok := v.(bool)
   	if !ok {
   		return false, errors.New("filter result is invalid")
   	}
   	return res, nil
   }

   This seems to call the overloaded function for all == operators. Although this does not affect my business, I still wonder if there is a way to overload just for the json.Number type
   By the way, I tried to use n.Left.Type().AssignableTo() like https://expr-lang.org/docs/patch#advanced-example mentioned but it seems doesn't work
3. expr-lang

   locked and limited conversation to collaborators on Sep 18, 2025
4. antonmedv

   converted this issue into a discussion #838 on Sep 18, 2025