fix: use once cell instead of lazy static (#35)

Author: xx01cyx

optd-cost-model/Cargo.lock

@@ -13,7 +13,6 @@ datafusion-expr = "32.0.0"
 ordered-float = "4.0"
 chrono = "0.4"
 itertools = "0.13"
-lazy_static = "1.5"
 
 [dev-dependencies]
 crossbeam = "0.8"

optd-cost-model/Cargo.toml

@@ -7,10 +7,7 @@
 //! Non-alpha-numeric characters are relegated to the end of the encoded value,
 //! rendering them indistinguishable from one another in this context.
 
-use std::collections::HashMap;
-
-// TODO: Use lazy cell instead of lazy static.
-use lazy_static::lazy_static;
+use std::{collections::HashMap, sync::LazyLock};
 
 // The alphanumerical ordering.
 const ALPHANUMERIC_ORDER: [char; 95] = [
@@ -23,16 +20,14 @@ const ALPHANUMERIC_ORDER: [char; 95] = [
 
 const PMF: f64 = 1.0 / (ALPHANUMERIC_ORDER.len() as f64);
 
-lazy_static! {
-    static ref CDF: HashMap<char, f64> = {
-        let length = ALPHANUMERIC_ORDER.len() + 1; // To account for non-alpha-numeric characters.
-        let mut cdf = HashMap::with_capacity(length);
-        for (index, &char) in ALPHANUMERIC_ORDER.iter().enumerate() {
-            cdf.insert(char, (index as f64) / (length as f64));
-        }
-        cdf
-    };
-}
+static CDF: LazyLock<HashMap<char, f64>> = LazyLock::new(|| {
+    let length = ALPHANUMERIC_ORDER.len() + 1; // To account for non-alpha-numeric characters.
+    let mut cdf = HashMap::with_capacity(length);
+    for (index, &char) in ALPHANUMERIC_ORDER.iter().enumerate() {
+        cdf.insert(char, (index as f64) / (length as f64));
+    }
+    cdf
+});
 
 pub fn encode(string: &str) -> f64 {
     let mut left = 0.0;