Laravel's pluck method recently got closure support in PR #56188. This is the usage example given:

Country::get()
    ->pluck(fn (Country $country) => "{$country->flag} {$country->name}", 'id')

Before this PR to achieve the same thing, you needed something like this:

Country::get()
    ->mapWithKeys(function (Country $country) {
        return [
            $city->id => "{$country->flag} - {$country->name}"
        ];
    });

I prefer a different approach altogether. I prefer to do a map() and keyBy() as separate operations:

Country::get()
    ->keyBy(static fn (Country $country): int => $country->id)
    ->map(static fn (Country $country): string => "{$country->flag} - {$country->name}");

The primary benefit of a dual-step approach is readability. Each line has its own responsibility, one for keys, one for values.

There are other subtle benefits too, for example accessing properties rather than magic 'id' strings or destructured arrays means IDEs and static analysers have a much easier job helping to prevent bugs or do refactoring. It also gives strong type guarantees for both the key and the value thanks to the closure return type declarations.

What about performance!?!

I'm sure some people will scoff at using keyBy() + map() because it means that every record is looped over twice and that's inefficient! To them I say how many rows do you have? Go count them. If it's less than a million, then stop worrying, if it's more benchmark it.