Edited the Strings
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# String
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`std::string::String` is a UTF-8 encoded, growable string. It is the most common string type we used in daily dev, it also has ownership over the string contents.
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`std::string::String` is a UTF-8 encoded, growable string. It is the most common string type we used in daily development, it also has ownership over the string contents.
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### Basic operations
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1. 🌟🌟
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@ -7,7 +7,7 @@
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// FILL in the blanks and FIX errors
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// 1. Don't use `to_string()`
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// 2. Dont't add/remove any code line
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// 2. Don't add/remove any code line
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fn main() {
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let mut s: String = "hello, ";
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s.push_str("world".to_string());
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@ -17,7 +17,7 @@ fn main() {
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assert_eq!(s, "hello, world!");
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println!("Success!")
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println!("Success!");
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}
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fn move_ownership(s: String) {
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@ -36,7 +36,7 @@ A `String` is stored as a vector of bytes (`Vec<u8>`), but guaranteed to always
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fn main() {
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let mut s = String::from("hello, world");
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let slice1: &str = __; // in two ways
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let slice1: &str = __; // In two ways
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assert_eq!(slice1, "hello, world");
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let slice2 = __;
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@ -46,37 +46,37 @@ fn main() {
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slice3.push('!');
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assert_eq!(slice3, "hello, world!");
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println!("Success!")
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println!("Success!");
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}
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```
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3. 🌟🌟
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```rust,editable
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// Question: how many heap allocations are happened here ?
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// Question: how many heap allocations are happening here?
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// Your answer:
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fn main() {
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// Create a String type based on `&str`
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// the type of string literals is `&str`
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// The type of string literals is `&str`
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let s: String = String::from("hello, world!");
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// create a slice point to String `s`
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// Create a slice point to String `s`
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let slice: &str = &s;
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// create a String type based on the recently created slice
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// Create a String type based on the recently created slice
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let s: String = slice.to_string();
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assert_eq!(s, "hello, world!");
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println!("Success!")
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println!("Success!");
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}
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```
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### UTF-8 & Indexing
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Strings are always valid UTF-8. This has a few implications:
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- the first of which is that if you need a non-UTF-8 string, consider [OsString](https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html). It is similar, but without the UTF-8 constraint.
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- The second implication is that you cannot index into a String
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- The first of which is that if you need a non-UTF-8 string, consider [OsString](https://doc.rust-lang.org/stable/std/ffi/struct.OsString.html). It is similar, but without the UTF-8 constraint.
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- The second implication is that you cannot index into a String.
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Indexing is intended to be a constant-time operation, but UTF-8 encoding does not allow us to do this. Furthermore, it’s not clear what sort of thing the index should return: a byte, a codepoint, or a grapheme cluster. The bytes and chars methods return iterators over the first two, respectively.
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let slice1 = s[0]; //tips: `h` only takes 1 byte in UTF8 format
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assert_eq!(slice1, "h");
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let slice2 = &s[3..5];// tips: `中` takes 3 bytes in UTF8 format
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let slice2 = &s[3..5]; // Tips: `中` takes 3 bytes in UTF8 format
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assert_eq!(slice2, "世");
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// iterate all chars in s
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// Iterate through all chars in s
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for (i, c) in s.__ {
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if i == 7 {
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assert_eq!(c, '世')
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}
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}
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println!("Success!")
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println!("Success!");
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}
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```
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#### utf8_slice
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#### UTF8_slice
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You can use [utf8_slice](https://docs.rs/utf8_slice/1.0.0/utf8_slice/fn.slice.html) to slice UTF8 string, it can index chars instead of bytes.
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**Example**
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let mut s = String::new();
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__;
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// some bytes, in a vector
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// Some bytes, in a vector
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let v = vec![104, 101, 108, 108, 111];
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// Turn a bytes vector into a String
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// Turn a byte's vector into a String
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let s1 = __;
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assert_eq!(s, s1);
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println!("Success!")
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println!("Success!");
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}
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```
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@ -151,7 +151,7 @@ The pointer points to an internal buffer String uses to store its data. The leng
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6. 🌟🌟 If a String has enough capacity, adding elements to it will not re-allocate
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```rust,editable
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// modify the code below to print out:
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// Modify the code below to print out:
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// 25
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// 25
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// 25
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println!("{}", s.capacity());
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}
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println!("Success!")
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println!("Success!");
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}
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```
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@ -179,7 +179,7 @@ use std::mem;
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fn main() {
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let story = String::from("Rust By Practice");
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// Prevent automatically dropping the String's data
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// Prevent automatically dropping of the String's data
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let mut story = mem::ManuallyDrop::new(story);
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let ptr = story.__();
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assert_eq!(16, len);
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// We can re-build a String out of ptr, len, and capacity. This is all
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// We can rebuild a String out of ptr, len, and capacity. This is all
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// unsafe because we are responsible for making sure the components are
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// valid:
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let s = unsafe { String::from_raw_parts(ptr, len, capacity) };
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assert_eq!(*story, s);
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println!("Success!")
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println!("Success!");
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}
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```
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