* Eradicate IndexDistance associated type, replacing with Int everywhere
* Consistently use Int for ExistentialCollection’s IndexDistance type.
* Fix test for IndexDistance removal
* Remove a handful of no-longer-needed explicit types
* Add compatibility shims for non-Int index distances
* Test compatibility shim
* Move IndexDistance typealias into the Collection protocol
After changes to stdlib and type-checker related to removing
of the `_Strideable` it's now possible to properly support
iterator types for *ClosedRange without any workarounds.
Resolves: rdar://problem/25584401
From the Swift documentation:
"If you define an optional variable without providing a default value,
the variable is automatically set to nil for you."
Changes:
- Moved only-used-once helper methods into call sites
- Parameterized tests that might expect a crash
- Fixed some comments and formatting; renamed some test helper APIs
* [stdlib] Implementing O(1) methods on `CountableClosedRange`
Changes:
- Implemented O(1) `index(_:offsetBy:)` and `distance(from:to:)` methods on `CountableClosedRange`
- Fixed some unit tests
- Added many more unit tests for Countable*Range index APIs
* Clarify test intent
The RangeProtocol was a very weak and fragile abstraction because it
didn't specify the interpretation of the endpoints. To write a
non-trivial algorithm, one usually needed to consult that information.
The standard library code only actually worked correctly with half-open
and closed ranges (and didn't handle fully open ranges, for example).
The other two protocols, HalfOpenRangeProtocol and ClosedRangeProtocol,
were only used for code sharing, and present an ABI burden. We can use
gyb instead.
