fix: use map func to avoid copy of string

solutions/generics-traits/const-generics.md

@@ -53,7 +53,7 @@ fn main() {
     check_size([0u8; 767]); 
     check_size([0i32; 191]);
     check_size(["hello你好"; 47]); // &str is a string reference, containing a pointer and string length in it, so it takes two word long, in x86-64, 1 word = 8 bytes
-    check_size(["hello你好".to_string(); 31]);  // String is a smart pointer struct, it has three fields: pointer, length and capacity, each takes 8 bytes
+    check_size([(); 31].map(|_| "hello你好".to_string()));  // String is a smart pointer struct, it has three fields: pointer, length and capacity, each takes 8 bytes
     check_size(['中'; 191]); // A char takes 4 bytes in Rust
 }