Kotlin: How apply all list elements to the object?

Question

I have such kotlin code. I didn't write it very elegantly, but it works correctly. How can I write this more beautifully using kotlin tools?

I need to apply all elements from the filters list to the query object.

fun create(filters: List<FilterFactory.Filter>, searchQuery: SearchQuery): Query {
    var query = Query()
    filters.forEach { filter -> query = filter.apply(query) }

    return query
}

Answer 1

You can refactor the implementation of the function by using fold here:

fun create(filters: List<FilterFactory.Filter>): Query =
    filters.fold(Query()) { q, f -> f.apply(q) }

Note that your initial code didn't make use of the searchQuery parameter, so I removed it.

As for the API, you might want to use an extension function instead, with the toX() convention for the name. For instance:

fun List<FilterFactory.Filter>.toQuery(): Query =
    fold(Query()) { q, f -> f.apply(q) }

toQuery() on a list of filters might be confusing to some, though. Maybe a better approach would be an extension on Query itself:

fun Query.withFilters(filters: List<FilterFactory.Filter>): Query =
    filters.fold(this) { q, f -> f.apply(q) }

Then to use it you'll need to provide the initial Query instance on the call site:

val filteredQuery = Query().withFilters(filters)