Move first OnceLock example to LazyLock

This example is spiritually an example of LazyLock, as it computes a
variable at runtime but accepts no inputs into that process.
It is also slightly simpler and thus easier to understand.
Change it to an even-more concise version and move it to LazyLock.

The example now editorializes slightly more. This may be unnecessary,
but it can be educational for the reader.

Author: workingjubilee

library/std/src/sync/lazy_lock.rs

@@ -29,34 +29,26 @@ union Data<T, F> {
 /// # Examples
 ///
 /// Initialize static variables with `LazyLock`.
-///
 /// ```
-/// use std::collections::HashMap;
-///
 /// use std::sync::LazyLock;
 ///
-/// static HASHMAP: LazyLock<HashMap<i32, String>> = LazyLock::new(|| {
-///     println!("initializing");
-///     let mut m = HashMap::new();
-///     m.insert(13, "Spica".to_string());
-///     m.insert(74, "Hoyten".to_string());
-///     m
+/// // n.b. static items do not call [`Drop`] on program termination, so this won't be deallocated.
+/// // this is fine, as the OS can deallocate the terminated program faster than we can free memory
+/// // but tools like valgrind might report "memory leaks" as it isn't obvious this is intentional.
+/// static DEEP_THOUGHT: LazyLock<String> = LazyLock::new(|| {
+/// # mod another_crate {
+/// #     pub fn great_question() -> String { "42".to_string() }
+/// # }
+///     // M3 Ultra takes about 16 million years in --release config
+///     another_crate::great_question()
 /// });
 ///
-/// fn main() {
-///     println!("ready");
-///     std::thread::spawn(|| {
-///         println!("{:?}", HASHMAP.get(&13));
-///     }).join().unwrap();
-///     println!("{:?}", HASHMAP.get(&74));
-///
-///     // Prints:
-///     //   ready
-///     //   initializing
-///     //   Some("Spica")
-///     //   Some("Hoyten")
-/// }
+/// // The `String` is built, stored in the `LazyLock`, and returned as `&String`.
+/// let _ = &*DEEP_THOUGHT;
+/// // The `String` is retrieved from the `LazyLock` and returned as `&String`.
+/// let _ = &*DEEP_THOUGHT;
 /// ```
+///
 /// Initialize fields with `LazyLock`.
 /// ```
 /// use std::sync::LazyLock;

library/std/src/sync/once_lock.rs

@@ -13,42 +13,6 @@ use crate::sync::Once;
 ///
 /// # Examples
 ///
-/// Using `OnceLock` to store a function’s previously computed value (a.k.a.
-/// ‘lazy static’ or ‘memoizing’):
-///
-/// ```
-/// use std::sync::OnceLock;
-///
-/// struct DeepThought {
-///     answer: String,
-/// }
-///
-/// impl DeepThought {
-/// #   fn great_question() -> String {
-/// #       "42".to_string()
-/// #   }
-/// #
-///     fn new() -> Self {
-///         Self {
-///             // M3 Ultra takes about 16 million years in --release config
-///             answer: Self::great_question(),
-///         }
-///     }
-/// }
-///
-/// fn computation() -> &'static DeepThought {
-///     // n.b. static items do not call [`Drop`] on program termination, so if
-///     // [`DeepThought`] impls Drop, that will not be used for this instance.
-///     static COMPUTATION: OnceLock<DeepThought> = OnceLock::new();
-///     COMPUTATION.get_or_init(|| DeepThought::new())
-/// }
-///
-/// // The `DeepThought` is built, stored in the `OnceLock`, and returned.
-/// let _ = computation().answer;
-/// // The `DeepThought` is retrieved from the `OnceLock` and returned.
-/// let _ = computation().answer;
-/// ```
-///
 /// Writing to a `OnceLock` from a separate thread:
 ///
 /// ```