expr/operator-dot.go

// Copyright (c) 2024 Celestino Amoroso (celestino.amoroso@gmail.com).
// All rights reserved.

// operator-dot.go
package expr

import "fmt"

// -------- dot term
func newDotTerm(tk *Token) (inst *term) {
	return &term{
		tk:       *tk,
		children: make([]*term, 0, 2),
		position: posInfix,
		priority: priDot,
		evalFunc: evalDot,
	}
}

func verifyIndex(indexTerm *term, indexValue any, maxValue int) (index int, err error) {
	var v int
	if v, err = indexTerm.toInt(indexValue, "index expression value must be integer"); err == nil {
		if v >= 0 && v < maxValue {
			index = v
		} else if index >= -maxValue {
			index = maxValue + v
		} else {
			err = indexTerm.Errorf("index %d out of bounds", v)
		}
	}
	return
}

func evalDot(ctx ExprContext, self *term) (v any, err error) {
	var leftValue, rightValue any

	if leftValue, rightValue, err = self.evalInfix(ctx); err != nil {
		return
	}

	indexTerm := self.children[1]

	switch unboxedValue := leftValue.(type) {
	case []any:
		var index int
		if index, err = verifyIndex(indexTerm, rightValue, len(unboxedValue)); err == nil {
			v = unboxedValue[index]
		}
	case string:
		var index int
		if index, err = verifyIndex(indexTerm, rightValue, len(unboxedValue)); err == nil {
			v = unboxedValue[index]
		}
	case map[any]any:
		var ok bool
		if v, ok = unboxedValue[rightValue]; !ok {
			err = fmt.Errorf("key %v does not belong to the dictionary", rightValue)
		}
	default:
		err = self.errIncompatibleTypes(leftValue, rightValue)
	}
	return
}

// init
func init() {
	registerTermConstructor(SymDot, newDotTerm)
}