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

[Xiaodi Wu]

Can you give some other examples of generic algorithms that would make use
of this DefaultConstructible? I'm having trouble coming up with any other
than reduce.
On Sun, Dec 25, 2016 at 14:23 Adam Nemecek via swift-evolution <
swift-evolution at swift.org> wrote:

> This protocol is present in C++
> http://en.cppreference.com/w/cpp/concept/DefaultConstructible as well as
> in Rust https://doc.rust-lang.org/std/default/
>
> It's the identity element/unit of a monoid or a zero.
>
> The Swift implementation is very simple (I'm open to different names)
>
> protocol DefaultConstructible {
>     init()
> }
>
> A lot of the standard types could then be made to conform to this
> protocol. These include all the numeric types, collection types (array,
> set, dict), string, basically at least every type that currently has a
> constructor without any arguments.
>
> The RangeReplaceableCollection protocol would inherit from this protocol
> as well.
>
> This protocol would simplify a lot of generic algorithms where you need
> the concept of a zero (which shows up a lot)
>
> Once introduced, Sequence could define an alternative implementation of
> reduce where the initial result doesn't need to be provided as it can be
> default constructed.
>
>
>
>
>
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