1ac3c983bf Mark single-argument constructors "explicit" (practicalswift)
Pull request description:
Mark single-argument constructors `explicit`.
Rationale:
* Avoid unexpected implicit promotions.
From the developer notes:
> **By default, declare single-argument constructors explicit.**
> Rationale: This is a precaution to avoid unintended conversions that might arise when single-argument constructors are used as implicit conversion functions.
Tree-SHA512: 7901ed5be808c9d0ecb5ca501e1bc0395987fe1b7941b8548cebac2ff08a14f7dab61fab374a69b9ba29a9295a04245c814325c7f95b97ae558af0780f111dfa
