Expand guide-level

Author: c410-f3r

text/2978-stack_based_vec.md

@@ -33,56 +33,76 @@ Just like `Vec`, `ArrayVec` is also a primitive vector where high-level structur
 # Guide-level explanation
 [guide-level-explanation]: #guide-level-explanation
 
-Instead of relying on a heap-allocator, stack-based memory area is added and removed on-demand in a last-in-first-out (LIFO) order according to the calling workflow of a program. Let's illustrate an imaginary function `super()` that allocates 32 bits before calling another function named `sub()` that also allocates 32 bits of auxiliary memory:
+`ArrayVec` is a container that encapsulates fixed size buffers. 
 
-```txt
-0 bits           32 bits          64 bits   
+```rust
+let mut v: ArrayVec<i32, 4> = ArrayVec::new();
+let _ = v.push(1);
+let _ = v.push(2);
+
+assert_eq!(v.len(), 2);
+assert_eq!(v[0], 1);
+
+assert_eq!(v.pop(), Some(2));
+assert_eq!(v.len(), 1);
+
+v[0] = 7;
+assert_eq!(v[0], 7);
 
+v.extend([1, 2, 3].iter().copied());
 
-|       |   ->   |       |   ->   |       |
----------        ---------        ---------
-                 | super |        |  sub  |
-                 ---------        ---------
-                                  | super |
-                                  ---------
+for element in &v {
+    println!("{}", element);
+}
+assert_eq!(v, [7, 1, 2, 3]);
 ```
 
-* Now `super()` returns and the exactly same thing happens in reverse order, dropping everything when out of scope.
+Instead of relying on a heap-allocator, stack-based memory area is added and removed on-demand in a last-in-first-out (LIFO) order according to the calling workflow of a program. `ArrayVec` takes advantage of this predictable behavior to reserve an exactly amount of uninitialized bytes up-front and these bytes form a buffer where elements can be included dynamically.
 
-```txt
-64 bits          32 bits          0 bits   
+```rust
+// `array_vec` can store up to 64 elements
+let mut array_vec: ArrayVec<i32, 64> = ArrayVec::new();
+```
 
+Of course, fixed buffers lead to inflexibility because unlike `Vec`, the underlying capacity can not expand at run-time and there will never be more than 64 elements in the above example.
 
-|       |   ->   |       |   ->   |       |
----------        ---------        ---------
-|  sub  |        | super |
----------        ---------
-| super |
----------
+```rust
+// This vector can store up to 0 elements, therefore, nothing at all
+let mut array_vec: ArrayVec<i32, 0> = ArrayVec::new();
+let push_result = array_vec.push(1);
+// Ooppss... Our push operation wasn't successful
+assert!(push_result.is_err());
 ```
 
-`ArrayVec` takes advantage of this predictable behavior to reserve an exactly amount of uninitialized bytes up-front and these bytes form a buffer where elements can be included dynamically.
+A good question is: Should I use `core::collections::ArrayVec<T>` or `alloc::collections::Vec<T>`? Well, `Vec` is already good enough for most situations while stack allocation usually shines for small sizes.
+
+* Do you have a known upper bound?
+
+* How much memory are you going to allocate for your program? The default values of `RUST_MIN_STACK` or `ulimit -s` might not be enough.
+
+* Are you using nested `Vec`s? `Vec<ArrayVec<T, N>>` might be better than `Vec<Vec<T>>`.
+
+Each use-case is different and should be pondered individually. In case of doubt, stick with `Vec`.
+
+For a more technical overview, take a look at the following operations:
 
 ```rust
-fn main() {
-    // `array_vec` has a pre-allocated memory of 2048 bits that can store up to 64 decimals.
-    let mut array_vec: ArrayVec<i32, 64> = ArrayVec::new();
+// `array_vec` has a pre-allocated memory of 2048 bits (32 * 64) that can store up
+// to 64 decimals.
+let mut array_vec: ArrayVec<i32, 64> = ArrayVec::new();
 
-    // Although reserved, there isn't anything explicitly stored yet
-    assert_eq!(array_vec.len(), 0);
+// Although reserved, there isn't anything explicitly stored yet
+assert_eq!(array_vec.len(), 0);
 
-    // Initializes the first 32 bits with a simple '1' decimal or
-    // 00000000 00000000 00000000 00000001 bits
-    array_vec.push(1);
+// Initializes the first 32 bits with a simple '1' decimal or
+// 00000000 00000000 00000000 00000001 bits
+array_vec.push(1);
 
-    // Our vector memory is now split into a 32/2016 pair of initialized and
-    // uninitialized memory respectively
-    assert_eq!(array_vec.len(), 1);
-}
+// Our vector memory is now split into a 32/2016 pair of initialized and
+// uninitialized memory respectively
+assert_eq!(array_vec.len(), 1);
 ```
 
-Of course, fixed buffers lead to some inflexibility because unlike `Vec`, the underlying capacity can not expand at run-time and there will never be more than 64 elements in the above example.
-
 # Reference-level explanation
 [reference-level-explanation]: #reference-level-explanation
 
@@ -189,8 +209,6 @@ impl<T, const N: usize> ArrayVec<T, N> {
 }
 ```
 
-Since it is known at compile-time the upper capacity bound, the compiler is likely going to remove the conditional bounding checking of the newly 
-
 Meaningless, unstable and deprecated methods like `reserve` or `drain_filter` weren't considered. A concrete implementation is available at https://github.com/c410-f3r/stack-based-vec.
 
 # Drawbacks
@@ -230,11 +248,11 @@ Should it be included in the prelude?
 ### Macros
 
 ```rust
-    // Instance with 1i32, 2i32 and 3i32
-    let _: ArrayVec<i32, 33> = array_vec![1, 2, 3];
+// Instance with 1i32, 2i32 and 3i32
+let _: ArrayVec<i32, 33> = array_vec![1, 2, 3];
 
-    // Instance with 1i32 and 1i32
-    let _: ArrayVec<i32, 64> = array_vec![1; 2];
+// Instance with 1i32 and 1i32
+let _: ArrayVec<i32, 64> = array_vec![1; 2];
 ```
 
 # Future possibilities