no constant folding

benches/my_benchmark.rs

@@ -2,12 +2,15 @@ use criterion::{black_box, criterion_group, criterion_main, Criterion};
 
 use rust_benchmark::{concat_with_format, concat_with_plus};
 
+const A: &str = "post";
+const B: &str = "/fasjhiofasihofas";
+
 pub fn criterion_benchmark(c: &mut Criterion) {
-    c.bench_function("concat with format", |b| {
-        b.iter(|| concat_with_format());
-    });
     c.bench_function("concat with plus", |b| {
-        b.iter(|| concat_with_plus());
+        b.iter(|| concat_with_plus(black_box(A), black_box(B)));
+    });
+    c.bench_function("concat with format", |b| {
+        b.iter(|| concat_with_format(black_box(A), black_box(B)));
     });
 }
 

src/lib.rs

@@ -1,20 +1,17 @@
-const A: &str = "post";
+pub fn concat_with_format(a: &str, b: &str) -> String {
-const B: &str = "/fasjhiofasihofas";
+    let c = format!("{} {}", a, b);
+    c
+}
+
+pub fn concat_with_plus(a: &str, b: &str) -> String {
+    let c = a.to_string() + " " + b;
+    c
+}
 
 pub fn add(left: usize, right: usize) -> usize {
     left + right
 }
 
-pub fn concat_with_plus() -> String {
-    let c = A.to_string() + " " + B;
-    c
-}
-
-pub fn concat_with_format() -> String {
-    let c = format!("{} {}", A, B);
-    c
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;