chained builder pattern

src/ch10_patterns/builder.rs

@@ -0,0 +1,44 @@
+struct StringBuilder<'a> {
+    segments: Vec<&'a str>,
+}
+
+impl<'a> StringBuilder<'a> {
+    pub fn new() -> Self {
+        StringBuilder { segments: vec![] }
+    }
+
+    pub fn append(mut self, segment: &'a str) -> Self {
+        self.segments.push(&segment);
+        self
+    }
+}
+
+impl<'a> From<StringBuilder<'a>> for String {
+    fn from(builder: StringBuilder<'a>) -> Self {
+        builder.segments.into_iter().collect()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_it_builds() {
+        // This is bad. Just use String::push_str
+        // Same thing that String::collect and String::extend do
+        // https://doc.rust-lang.org/src/alloc/string.rs.html#1758-1764
+
+        let b = StringBuilder::new()
+            .append("This ")
+            .append("could be ")
+            .append("very long ")
+            .append("and blow up ")
+            .append("your program");
+
+        assert_eq!(
+            String::from(b),
+            String::from("This could be very long and blow up your program"),
+        )
+    }
+}

src/ch10_patterns/mod.rs

@@ -0,0 +1 @@
+pub mod builder;

src/lib.rs

@@ -13,3 +13,4 @@ pub mod ch06_datastructures;
 pub mod ch07_algorithms;
 pub mod ch08_adv_algs;
 pub mod ch09_compiler;
+pub mod ch10_patterns;