src/precore/util/FluentIterable.php
public function transformAndConcat(callable $transformer) : FluentIterable
    {
        return self::from(Iterables::concatIterables($this->transform($transformer)));
    }
public function transformAndConcat(callable $transformer) : FluentIterable
    {
        return self::from(Iterables::concatIterables($this->transform($transformer)));
    }
Applies function to each element of this fluent iterable and returns a fluent iterable
with the concatenated combination of results. Transformer returns a Traversable of results.

@param callable $transformer
@return FluentIterable
@see flatMap