{"record":{"id":"54c2bc5af6093ade","repo":"apache/beam","slug":"too-few-params","errorCode":null,"errorMessage":"too few params","messagePattern":"too few params","errorType":"validation","errorClass":null,"httpStatus":null,"severity":"error","filePath":"sdks/go/pkg/beam/core/graph/bind.go","lineNumber":151,"sourceCode":"}\n\nfunc findInbound(fn *funcx.Fn, in ...typex.FullType) ([]typex.FullType, []InputKind, error) {\n\t// log.Printf(\"Bind inbound: %v %v\", fn, in)\n\taddContext := func(err error, p []funcx.FnParam, in any) error {\n\t\treturn errors.WithContextf(err, \"binding params %v to input %v\", p, in)\n\t}\n\n\tvar inbound []typex.FullType\n\tvar kinds []InputKind\n\tparams := funcx.SubParams(fn.Param, fn.Params(funcx.FnValue|funcx.FnIter|funcx.FnReIter|funcx.FnMultiMap)...)\n\tindex := 0\n\tfor _, input := range in {\n\t\tarity, err := inboundArity(input, index == 0)\n\t\tif err != nil {\n\t\t\treturn nil, nil, addContext(err, params, input)\n\t\t}\n\t\tif len(params)-index < arity {\n\t\t\treturn nil, nil, addContext(errors.New(\"too few params\"), params[index:], input)\n\t\t}\n\n\t\tparamsToBind := params[index : index+arity]\n\t\telm, kind, err := tryBindInbound(input, paramsToBind, index == 0)\n\t\tif err != nil {\n\t\t\treturn nil, nil, addContext(err, paramsToBind, input)\n\t\t}\n\t\tinbound = append(inbound, elm)\n\t\tkinds = append(kinds, kind)\n\t\tindex += arity\n\t}\n\tif index < len(params) {\n\t\treturn nil, nil, addContext(errors.New(\"too few inputs: forgot an input or to annotate options?\"), params, in)\n\t}\n\tif index > len(params) {\n\t\treturn nil, nil, addContext(errors.New(\"too many inputs\"), params, in)\n\t}\n\treturn inbound, kinds, nil","sourceCodeStart":133,"sourceCodeEnd":169,"githubUrl":"https://github.com/apache/beam/blob/12126d8942aaf848030c478b4c6a28c6af861c66/sdks/go/pkg/beam/core/graph/bind.go#L133-L169","documentation":"During graph construction, Bind/findInbound matches supplied runtime parameters (inputs, side inputs, options) to the function's declared inbound arity. This error means the list of parameters ran out: a remaining input requires `arity` params but fewer than that remain, so the function call cannot be fully bound.","triggerScenarios":"Calling beam.ParDo/beam.Combine/etc. with a DoFn or function whose signature requires more main/side inputs than were passed — e.g. a DoFn with ProcessElement(ctx, element, sideInput) bound with only two arguments, or forgetting a side-input argument.","commonSituations":"Forgetting to pass a side input created with beam.SideInput, omitting the emitter/emitter-out argument order mismatch, or changing a DoFn signature without updating the transform call site.","solutions":["Pass all required inputs to the transform in signature order (main element first, then side inputs, then options).","Compare the DoFn ProcessElement signature arity with the arguments supplied at the beam.ParDo/beam.TryParDo call site.","If the extra input is a side input, wrap it with beam.SideInput(pcoll) and pass it in the right position.","Use beam.TryParDo to get a clearer typed error during development."],"exampleFix":"// before\nbeam.ParDo(s, &myFn{}, in)          // myFn needs a side input\n// after\nbeam.ParDo(s, &myFn{}, in, beam.SideInput{Input: side})","handlingStrategy":"validation","validationCode":"// Count main + side input params of the DoFn and compare with args before binding\nif len(args) < requiredArity(dofn) {\n    return fmt.Errorf(\"%s requires %d inputs, got %d\", dofnName, requiredArity(dofn), len(args))\n}","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Match every ProcessElement input parameter with a corresponding transform argument, in order.","Wrap side inputs with beam.SideInput{} and pass them after main inputs.","Use beam.TryParDo during development for clearer arity/type errors."],"tags":["go","beam","graph","arity-mismatch"],"backgroundTag":"missing-required-argument","analyzedSha":"12126d8942aaf848030c478b4c6a28c6af861c66","analyzedAt":"2026-09-13T01:50:10.254Z","contentChangedAt":"2026-09-13T01:50:10.254Z","schemaVersion":2},"datasetVersion":"2026-09-14T16:17:12.679Z"}