[stdlib] Revise InlineArray documentation (#84978)

Update documentation for `InlineArray` to include examples with type
sugar, reword to avoid certain jargon that may be unfamiliar to some
standard library users, and incorporate additional details mostly drawn
from the proposal text.

---------

Co-authored-by: Alex Martini <amartini@apple.com>

Author: xwu

stdlib/public/core/InlineArray.swift

@@ -12,34 +12,88 @@
 
 /// A fixed-size array.
 ///
-/// The `InlineArray` type is a specialized array that stores its elements
-/// contiguously inline, rather than allocating an out-of-line region of memory
-/// with copy-on-write optimization.
+/// An `InlineArray` is a specialized container that doesn't use a separate
+/// memory allocation just to store its elements. When a value is copied, all of
+/// its elements are copied eagerly, like those of a tuple. Use an `InlineArray`
+/// when you have a fixed number of elements and need to avoid a separate heap
+/// allocation.
 ///
-/// Memory Layout
-/// -------------
+/// Initializing a Value
+/// --------------------
+///
+/// When initializing a new `InlineArray` value, you must initialize all of its
+/// elements. You can use an array literal just as with `Array`, rely on type
+/// inference for the `count` and `Element` type, and spell the type with the
+/// shorthand `[count of Element]`.
+///
+///     let a: InlineArray<3, Int> = [1, 2, 3]
+///     let b: InlineArray<_, Int> = [1, 2, 3]
+///     let c: InlineArray<3, _>   = [1, 2, 3]
+///     let d: InlineArray         = [1, 2, 3]
+///     
+///     let e: [3 of Int]          = [1, 2, 3]
+///     let f: [_ of Int]          = [1, 2, 3]
+///     let g: [3 of _]            = [1, 2, 3]
+///     let h: [_ of _]            = [1, 2, 3]
+///
+/// You can also use one of the type's initializers to create a new value.
+///
+/// Accessing Elements
+/// ------------------
+///
+/// Just as with `Array`, you can read and modify an element in an `InlineArray`
+/// using a subscript. Unless you use the memory-unsafe `unchecked` subscript,
+/// any index you provide is subject to bounds checking; an invalid index
+/// triggers a runtime error in your program.
 ///
-/// An *empty* array's size is zero. Its stride and alignment are one byte.
+///     var values: [3 of Double] = [1, 1.5, 2]
+///     print(values[0])  // Prints "1.0"
+///     values[1] -= 0.25
+///     print(values[1])  // Prints "1.25"
+///     values[3] = 42.0  // Fatal error: Index out of bounds
 ///
-/// A *nonempty* array's size and stride are equal to the element's stride
-/// multiplied by the number of elements. Its alignment is equal to the
-/// element's alignment.
+/// You can use the `indices` property to iterate over all elements in order.
+///
+///     for index in values.indices {
+///         print(values[index])
+///     }
+///
+/// Working with Noncopyable Elements
+/// ---------------------------------
+///
+/// An `InlineArray` can store elements of potentially noncopyable type. When
+/// `Element` isn't copyable, the `InlineArray` itself also isn't copyable. You
+/// must then explicitly move or consume the value if you want to transfer
+/// ownership.
+///
+/// Memory Layout
+/// -------------
 ///
-///     MemoryLayout<InlineArray<3, UInt16>>.size       //-> 6
-///     MemoryLayout<InlineArray<3, UInt16>>.stride     //-> 6
-///     MemoryLayout<InlineArray<3, UInt16>>.alignment  //-> 2
+/// An `InlineArray` stores its elements contiguously. If an `InlineArray` is a
+/// stored property of a class, then it's allocated on the heap along with the
+/// other stored properties of the class. Otherwise, in general, an
+/// `InlineArray` is allocated on the stack.
 ///
-/// Literal Initialization
-/// ----------------------
+/// A *non-empty* `InlineArray`'s size and stride are both found by multiplying
+/// the `count` of elements by the `Element`'s stride. Its alignment is equal to
+/// the `Element`'s alignment.
 ///
-/// Array literal syntax can be used to initialize an `InlineArray` instance.
-/// A stack-allocated array will do in-place initialization of each element.
-/// The `count` and/or `Element` can be inferred from the array literal.
+///     struct Record {
+///         let x: UInt32
+///         let y: Bool
+///     }
+///     MemoryLayout<Record>.size                 // 5
+///     MemoryLayout<Record>.stride               // 8
+///     MemoryLayout<Record>.alignment            // 4
+///     MemoryLayout<[2 of Record]>.size          // 16
+///     MemoryLayout<[2 of Record]>.stride        // 16
+///     MemoryLayout<[2 of Record]>.alignment     // 4
+///     MemoryLayout<(Record, Record)>.size       // 13
+///     MemoryLayout<(Record, Record)>.stride     // 16
+///     MemoryLayout<(Record, Record)>.alignment  // 4
 ///
-///     let a: InlineArray<4, Int> = [1, 2, 4, 8]
-///     let b: InlineArray<_, Int> = [1, 2, 4, 8]
-///     let c: InlineArray<4, _>   = [1, 2, 4, 8]
-///     let d: InlineArray         = [1, 2, 4, 8]
+/// An *empty* `InlineArray`'s size is zero. Its stride and alignment are both
+/// one byte.
 @available(SwiftStdlib 6.2, *)
 @frozen
 @safe
@@ -203,7 +257,7 @@ extension InlineArray where Element: ~Copyable {
   /// count of the array, to initialize every element by passing the closure
   /// the index of the current element being initialized.
   ///
-  ///     InlineArray<4, Int> { 1 << $0 }  //-> [1, 2, 4, 8]
+  ///     InlineArray<4, Int> { $0 * 2 }  // [0, 2, 4, 6]
   ///
   /// The closure is allowed to throw an error at any point during
   /// initialization at which point the array will stop initialization,
@@ -242,7 +296,7 @@ extension InlineArray where Element: ~Copyable {
   /// count of the array, to initialize every element by passing the closure an
   /// immutable borrow reference to the preceding element.
   ///
-  ///     InlineArray<4, Int>(first: 1) { $0 << 1 }  //-> [1, 2, 4, 8]
+  ///     InlineArray<4, Int>(first: 1) { $0 * 2 }  // [1, 2, 4, 8]
   ///
   /// The closure is allowed to throw an error at any point during
   /// initialization at which point the array will stop initialization,