[swift-evolution] It's the little things..

Chris Lattner clattner at apple.com
Tue Dec 13 11:51:02 CST 2016

On Dec 12, 2016, at 6:58 PM, David Sweeris via swift-evolution <swift-evolution at swift.org> wrote:
>> On Dec 12, 2016, at 16:15, John Holdsworth via swift-evolution <swift-evolution at swift.org> wrote:
>> I’d like to raise again the idea of optionality when referencing a key or
>> calling a function could be possible using a ? i.e instead of
>>   let a = key != nil ? dict[key] : nil
>> you could just write:
>>   let a = dict[key?]
>> or even 
>>   let a = func( arg: argumentThatMayBeNull? ) // not called if argument is nil
> The first part is pretty easy to add in an extension:
> extension Dictionary {
>    subscript(_ key:Key?) -> Value? {
>        return key != nil ? self[key!] : nil
>    }
> }
> At least I think that works... I'm on my phone so I can't test it.

You can do something like this, but I’d recommend labeling the subscript.  The problem comes up when you have a dictionary that has an optional key:   When you use “myDict[nil]”, you may get one or the other, but you probably mean one specifically.  

Using a label on the subscript solves this, and makes the code more explicit that you’re not just getting the normal subscript that everyone would expect.


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