Hmm, it looks like you’re right. I could swear I’ve used flatMap without a
closure before…oh well, looks like that’s what happens when you send code
without running it in a Playground.
Saagar Jha
> On Feb 13, 2017, at 5:33 PM, Jon Shier <j...@jonshier.com> wrote:
>
> According to the compiler, the closure argument for flatMap is not optional
> or defaulted, so it’s always required. I think it should default to { $0 },
> but whatever.
>
>
> Jon
>
>> On Feb 13, 2017, at 8:26 PM, Saagar Jha via swift-users
>> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote:
>>
>> flatMap was designed to work this way. How I rationalize it is that flatMap
>> “extracts” the value from an array’s elements and expands it. For an Array,
>> this is just taking out the individual Elements, but for an Optional, which
>> a “wrapper” around one value, it just takes this value out. Optionals with
>> no value (the .none case, or nil as it’s more commonly known) have nothing
>> to contribute and thus are filtered out.
>>
>> Saagar Jha
>>
>> P.S. You can call flatMap without a closure: deep.flatMap().flatMap()
>>
>>> On Feb 13, 2017, at 4:31 PM, Maxim Veksler via swift-users
>>> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote:
>>>
>>> Hi everyone,
>>>
>>> I've discovered today that Swift will actually choose 2 very differently
>>> behaving types of flatMap implementation based on the input signature.
>>>
>>> For a Sequence of options it will call a flatMap that filters out nil's.
>>> For a Sequence of Sequence's it will call a flattening function, without
>>> filtering.
>>>
>>> Leading to code that (IMHO) reads very not inconsistency, and unexpected.
>>> Sometime even looking a bit funny such as collection.flatMap.flatMap:
>>>
>>> 5> let deep = [["1989", nil], [nil, "Red"], [nil, nil]]
>>> deep: [[String?]] = 3 values {
>>> [0] = 2 values {
>>> [0] = "1989"
>>> [1] = nil
>>> }
>>> [1] = 2 values {
>>> [0] = nil
>>> [1] = "Red"
>>> }
>>> [2] = 2 values {
>>> [0] = nil
>>> [1] = nil
>>> }
>>> }
>>> 6> deep.flatMap { $0 }
>>> $R1: [String?] = 6 values {
>>> [0] = "1989"
>>> [1] = nil
>>> [2] = nil
>>> [3] = "Red"
>>> [4] = nil
>>> [5] = nil
>>> }
>>> 7> deep.flatMap { $0 }.flatMap { $0 }
>>> $R2: [String] = 2 values {
>>> [0] = "1989"
>>> [1] = "Red"
>>> }
>>> I wonder why it was implemented this way?
>>>
>>>
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>>
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