Method AddQualifier

interpreter/interpretable.go:1080–1119

AddQualifier creates a wrapper over the incoming qualifier which observes the qualification result.

(q Qualifier)

// AddQualifier creates a wrapper over the incoming qualifier which observes the qualification
// result.
func (e *evalWatchAttr) AddQualifier(q Qualifier) (Attribute, error) {
	switch qual := q.(type) {
	// By default, the qualifier is either a constant or an attribute
	// There may be some custom cases where the attribute is neither.
	case ConstantQualifier:
		// Expose a method to test whether the qualifier matches the input pattern.
		q = &evalWatchConstQual{
			ConstantQualifier: qual,
			observer:          e.observer,
			adapter:           e.Adapter(),
		}
	case *evalWatchAttr:
		// Unwrap the evalWatchAttr since the observation will be applied during Qualify or
		// QualifyIfPresent rather than Eval.
		q = &evalWatchAttrQual{
			Attribute: qual.InterpretableAttribute,
			observer:  e.observer,
			adapter:   e.Adapter(),
		}
	case Attribute:
		// Expose methods which intercept the qualification prior to being applied as a qualifier.
		// Using this interface ensures that the qualifier is converted to a constant value one
		// time during attribute pattern matching as the method embeds the Attribute interface
		// needed to trip the conversion to a constant.
		q = &evalWatchAttrQual{
			Attribute: qual,
			observer:  e.observer,
			adapter:   e.Adapter(),
		}
	default:
		// This is likely a custom qualifier type.
		q = &evalWatchQual{
			Qualifier: qual,
			observer:  e.observer,
			adapter:   e.Adapter(),
		}
	}
	_, err := e.InterpretableAttribute.AddQualifier(q)
	return e, err
}

// Exec implements the InterpretableV2 interface method.
func (e *evalWatchAttr) Exec(frame *ExecutionFrame) ref.Val {