refactor/polish ~ fix cargo clippy complaints (String => str)

src/pathchk/pathchk.rs

@@ -229,7 +229,7 @@ fn check_default(path: &[String]) -> bool {
 }
 
 // check whether a path is or if other problems arise
-fn check_searchable(path: &String) -> bool {
+fn check_searchable(path: &str) -> bool {
     // we use lstat, just like the original implementation
     match fs::symlink_metadata(path) {
         Ok(_) => true,
@@ -243,12 +243,12 @@ fn check_searchable(path: &String) -> bool {
 }
 
 // check for a hyphen at the beginning of a path segment
-fn no_leading_hyphen(path_segment: &String) -> bool {
+fn no_leading_hyphen(path_segment: &str) -> bool {
     !path_segment.starts_with('-')
 }
 
 // check whether a path segment contains only valid (read: portable) characters
-fn check_portable_chars(path_segment: &String) -> bool {
+fn check_portable_chars(path_segment: &str) -> bool {
     let valid_str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789._-".to_string();
     for ch in path_segment.chars() {
         if !valid_str.contains(ch) {

src/printf/memo.rs

@@ -25,7 +25,7 @@ fn warn_excess_args(first_arg: &str) {
 }
 
 impl Memo {
-    pub fn new(pf_string: &String, pf_args_it: &mut Peekable<Iter<String>>) -> Memo {
+    pub fn new(pf_string: &str, pf_args_it: &mut Peekable<Iter<String>>) -> Memo {
         let mut pm = Memo { tokens: Vec::new() };
         let mut tmp_token: Option<Box<dyn Token>>;
         let mut it = put_back_n(pf_string.chars());

src/printf/tokenize/num_format/num_format.rs

@@ -11,7 +11,7 @@ use super::formatters::cninetyninehexfloatf::CninetyNineHexFloatf;
 use super::formatters::scif::Scif;
 use super::formatters::decf::Decf;
 
-pub fn warn_expected_numeric(pf_arg: &String) {
+pub fn warn_expected_numeric(pf_arg: &str) {
     // important: keep println here not print
     cli::err_msg(&format!("{}: expected a numeric value", pf_arg));
 }