elliotchance/gedcom

package q

import (
    "reflect"
)

// CombineExpr will combine multiple slices of the same type into a single
// slice.
//
// If the slices are not the same type an error will be returned with a nil
// value.
type CombineExpr struct{}

func (e *CombineExpr) Evaluate(engine *Engine, input interface{}, args []*Statement) (interface{}, error) {
    if len(args) == 0 {
        return nil, nil
    }

    // Build a new slice with all elements.
    firstArg, err := args[0].Evaluate(engine, input)
    if err != nil {
        return nil, err
    }

    slice := reflect.MakeSlice(reflect.TypeOf(firstArg), 0, 0)
    for _, arg := range args {
        argValue, err := arg.Evaluate(engine, input)
        if err != nil {
            return nil, err
        }

        slice = reflect.AppendSlice(slice, reflect.ValueOf(argValue))
    }

    return slice.Interface(), nil
}