func Union() string {
	return `
func Union<FTYPE>(arrList ...[]<TYPE>) []<TYPE> {
	resultMap := make(map[<TYPE>]struct{})
	for _, arr := range arrList {
		for _, v := range arr {
			resultMap[v] = struct{}{}
		}
	}
	resultArr := make([]<TYPE>, len(resultMap))
	i := 0
	for k := range resultMap {
		resultArr[i] = k
		i++
	}
	return resultArr
}
`
}
Union is template.
package basic