box up FileEnv's functions

src/file/env.rs

@@ -1,15 +1,19 @@
 use std::fs::{File, OpenOptions};
 use std::io::Write;
 
+pub type FileOpenFn = Box<dyn Fn(&str) -> std::io::Result<File>>;
+
+pub type FileAppendLineFn = Box<dyn Fn(&str, &str) -> std::io::Result<()>>;
+
 pub struct FileEnv {
-    pub open: FileOpen,
-    pub append_line: FileAppendLine,
+    pub open: FileOpenFn,
+    pub append_line: FileAppendLineFn,
 }
 impl Default for FileEnv {
     fn default() -> Self {
         Self {
-            open: |path| File::open(path),
-            append_line: |file_name, line| {
+            open: Box::new(|path| File::open(path)),
+            append_line: Box::new(|file_name, line| {
                 let mut file = OpenOptions::new()
                     .write(true)
                     .append(true)
@@ -18,9 +22,7 @@ impl Default for FileEnv {
                     .unwrap();
                 writeln!(file, "{}", line)?;
                 Ok(())
-            },
+            }),
         }
     }
 }
-pub type FileOpen = fn(path: &str) -> std::io::Result<File>;
-pub type FileAppendLine = fn(paht: &str, line: &str) -> std::io::Result<()>;