CheckerContext

type CheckerContext struct {
    StructValue      reflect.Value
    FieldName        string
    FieldType        reflect.Type
    FieldValue       interface{}
    FieldLabel       string
    TemplateLanguage language.Tag
    Rule             *rule
}

The argument every checker receives. govalid populates it before calling your function — you don't construct it yourself in normal use.

Fields

Field	Description
StructValue	reflect.Value of the surrounding struct. Use this to access sibling fields by name.
FieldName	Go field name (not the label).
FieldType	reflect.Type of the field.
FieldValue	The actual value, ready to type-assert. May be nil for nil pointer/interface fields.
FieldLabel	Resolved label string (locale-aware).
TemplateLanguage	Active locale for the current Check call.
Rule	Pointer to the parsed rule. Rule.params is the []string of tag parameters.

Recipes

Read a tag parameter

if len(c.Rule.params) == 0 {
    return govalid.MakeCheckerParamError(c)
}
limit, err := strconv.Atoi(c.Rule.params[0])

Look up a sibling field

sv := c.StructValue
for i := 0; i < sv.Type().NumField(); i++ {
    if sv.Type().Field(i).Name == "Other" {
        v := sv.Field(i).Interface()
        // ...
    }
}

Type-assert with safety

v, ok := c.FieldValue.(string)
if !ok {
    return govalid.MakeValueTypeError(c)
}

Build a localized error

return govalid.NewErrorContext(c)

NewErrorContext reads c.Rule.checker to look up the right template, applies c.TemplateLanguage, and prefixes c.FieldLabel. You only need to register the message via SetMessageTemplates once.