[swift-evolution] Proposal: An assignment operator := that ensures nil before assignment.

[Taras Zakharko]

> On 27 Feb 2016, at 18:02, Amir Michail via swift-evolution <swift-evolution at swift.org> wrote:
>> 
> 
> Here’s a use case. Suppose you are filling out a dictionary in some non-trivial way. However, it should be the case that the value for each key is computed and assigned only once. And so you would use the := operator to ensure this: dictionary[k] := value

No, you would define an extension method for the Dictionary that does exactly this.

The issue I have with your proposal is that it suggests to introduce a new privileged syntax (a very unfortunate one at that)  for doing a very niche operation.  If you need this construct: define it in your code. If you think it is generally useful: suggest it as an extension to the standard library. However, I at least see no reason why this should be a primary privileged operation in the language grammar itself. 

— Taras
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