finish ch4, come back later

ch4/slice_type/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "slice_type"
+version = "0.1.0"

ch4/slice_type/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "slice_type"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

ch4/slice_type/src/main.rs

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+// Section 4.4
+// slices allow for reference in contiguous sequences of elements
+// inside of a collection.
+//
+// Part of writing fast Rust code is also understanding how
+// allocations work. This portion of the book is important, and I
+// need to come back and read it later.
+
+fn main() {
+    let mut s = String::from("hello world");
+    let word = first_word(&s);
+
+    // borrowed here. Not allowed
+    // s.clear();
+    // print!("word: {word}");
+
+    // Range syntax. the .. like Haskell
+    let s = String::from("hello");
+    let slice = &s[0..2];
+    let slice = &s[..2];
+    let slice = &s[..]; // can just slice the whole thing
+
+    // Is this possible?
+    // no
+    // let temp_arr_size = 5;
+    // let temparr = [1; temp_arr_size];
+}
+
+// This isn't part of the section, just me testing out ownership
+fn mod_string(s: &mut String) -> &String {
+    s.push_str("hello");
+    s
+}
+
+fn first_word(s: &String) -> &str {
+    let bytes = s.as_bytes();
+    for (i, &item) in bytes.iter().enumerate() {
+        if item == b' ' {
+            return &s[0..i];
+        }
+    }
+    &s[..]
+}
+
+// as.bytes() makes this an immutable reference
+// fn example_test() {
+//     let mut s = String::from("hello");
+//     for &item in s.as_bytes().iter() {
+//         if item == b'l' {
+//             s.push_str(" world");
+//         }
+//     }
+//     println!("{s}");
+// }