[swift-evolution] [Pitch] Add the DefaultConstructible protocol to the standard library

[David Sweeris]

> On Dec 26, 2016, at 11:35, Tony Allevato <allevato at google.com> wrote:
> 
> Mathematically, identities are associated with (type, operation) pairs, not types alone.
> 
> This conversation has put me in the column of "numeric types shouldn't have default initializers at all", personally.

I'd agree, except sometimes you need a T, any T, for when you want to create a "pre-sized" array for stuffing results into by index:
for i in ... {
    a[i] = ...
}
Simply saying "var a =[T](); a.reserveCapacity()" doesn't cut it because it'll still crash if you try to store anything in a[i] without somehow putting at least i+1 elements in the array first.

- Dave Sweeris
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