kataras/iris · error

bad value: %#+v

Error message

bad value: %#+v

What it means

newDependency panics when the value passed to Register/NewDependency is not of a usable kind (e.g. nil or an invalid reflect.Value). The hero DI container cannot build a Dependency from it, so it fails fast at registration time rather than at request time.

Source

Thrown at hero/dependency.go:100

func newDependency(
	dependency any,
	disablePayloadAutoBinding bool,
	enableStructDependents bool,
	matchDependency DependencyMatcher,
	funcDependencies ...*Dependency,
) *Dependency {
	if dependency == nil {
		panic(fmt.Sprintf("bad value: nil: %T", dependency))
	}

	if d, ok := dependency.(*Dependency); ok {
		// already a *Dependency, do not continue (and most importatly do not call resolveDependency) .
		return d
	}

	v := valueOf(dependency)
	if !goodVal(v) {
		panic(fmt.Sprintf("bad value: %#+v", dependency))
	}

	if matchDependency == nil {
		matchDependency = DefaultDependencyMatcher
	}

	dest := &Dependency{
		Source:           newSource(v),
		OriginalValue:    dependency,
		StructDependents: enableStructDependents,
	}
	dest.Match = ToDependencyMatchFunc(dest, matchDependency)

	if !resolveDependency(v, disablePayloadAutoBinding, dest, funcDependencies...) {
		panic(fmt.Sprintf("bad value: could not resolve a dependency from: %#+v", dependency))
	}

	return dest

View on GitHub (pinned to 7bedaf55a0)

Solutions

1. Ensure the value passed to Register/NewDependency is non-nil and of a supported kind (pointer, func, struct, base type value).
2. If registering a pointer, initialize it first: dep := &MyStruct{}; c.Register(dep).
3. Check that you are not accidentally passing a typed nil (e.g. var h *Handler; c.Register(h)).
4. Wrap registration in a helper that asserts non-nil before calling Register.

Example fix

// before
var logger *Logger // nil
c.Register(logger) // panics: bad value
// after
logger := NewLogger()
if logger == nil { panic("logger not initialized") }
c.Register(logger)

func safeRegister(c *hero.Container, v any) {
	if v == nil || reflect.ValueOf(v).IsZero() {
		panic("refusing to register nil/zero value")
	}
	c.Register(v)
}

func isRegisterable(v any) bool {
	rv := reflect.ValueOf(v)
	if !rv.IsValid() { return false }
	switch rv.Kind() {
	case reflect.Ptr, reflect.Interface, reflect.Map, reflect.Slice, reflect.Func, reflect.Chan:
		return !rv.IsNil()
	}
	return true
}

When it happens

Trigger: Calling c.Register(nil), registering an unexported/nil-valued variable, or passing a value whose reflect kind fails goodVal() (invalid, nil pointer/interface/func without proper signature) to NewDependency, Register, or via getBindingsForStruct.

Common situations: Config mistakes like registering a struct field that is a nil pointer because an init step failed, typos where a nil variable is passed instead of its address, or refactorings that removed the value assigned before registration.

Related errors

• bad value: nil: %T
• api container: set dependency matcher: fn cannot be nil
• bindings: unresolved: no a func type: %#+v
• expected [%d] bindings (input parameters) but got [%d] Funct
• bindings: unresolved: not a struct type: %#+v

AI-assisted analysis of kataras/iris@7bedaf55a0 (2026-08-30). Data as JSON: /api/errors/6215c4ba1fedd8ca. Report an issue: GitHub.