From 67cdcc2e12118becb823e20a40cc2687f2b8425a Mon Sep 17 00:00:00 2001
From: Adam Carpenter <53hornet@gmail.com>
Date: Wed, 27 Mar 2019 15:32:37 -0400
Subject: Started Rust in Action MEAP.

---
 meap/meap-code/ch2/ch2-introducing-vec.rs | 52 +++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 meap/meap-code/ch2/ch2-introducing-vec.rs

(limited to 'meap/meap-code/ch2/ch2-introducing-vec.rs')

diff --git a/meap/meap-code/ch2/ch2-introducing-vec.rs b/meap/meap-code/ch2/ch2-introducing-vec.rs
new file mode 100644
index 0000000..0a3cf4b
--- /dev/null
+++ b/meap/meap-code/ch2/ch2-introducing-vec.rs
@@ -0,0 +1,52 @@
+fn main() {
+  // PARAMETERS
+  let context_lines = 2;
+  let needle = "oo";
+  let haystack = "Every face, every shop,
+bedroom window, public-house, and
+dark square is a picture
+feverishly turned--in search of what?
+It is the same with books.
+What do we seek
+through millions of pages?";
+
+  // INITIALIZATION
+  let mut tags: Vec<usize> = Vec::new(); // <1> `tags` holds line numbers where matches occur
+  let mut ctx: Vec<Vec<(usize, String)>> = Vec::new(); // <2> `ctx` contains a vector per match to hold that match's context lines
+
+  // PASS 1
+  for (i, line) in haystack.lines().enumerate() { // <3> iterate through the lines, recording line numbers where matches are encountered
+    if line.contains(needle) {
+      tags.push(i);
+
+      let v = Vec::with_capacity(2*context_lines + 1); // <4> <5> `Vec::with_capacity(_n_)` reserves space for _n_ items
+      ctx.push(v);
+    }
+  }
+
+  if tags.len() == 0 { // <6> When there are no matches, exit early
+    return;
+  }
+
+  // PASS 2
+  for (i, line) in haystack.lines().enumerate() { // <7> For each tag, at every line, check to see if we are nearby a match. When we are, add that line to the relevant `Vec<T>` within `ctx`.
+    for (j, tag) in tags.iter().enumerate() {
+      let lower_bound = tag.saturating_sub(context_lines); // <8> `usize.saturating_sub()` returns 0, rather than underflowing
+      let upper_bound = tag + context_lines;
+
+      if (i >= lower_bound) && (i <= upper_bound) {
+          let line_as_string = String::from(line); // <9> Copy `line` into a new `String` and store that locally for each match
+          let local_ctx = (i, line_as_string);
+          ctx[j].push(local_ctx);
+      }
+    }
+  }
+
+  // OUTPUT
+  for local_ctx in ctx.iter() {
+    for &(i, ref line) in local_ctx.iter() { // <10> `ref line` informs the compiler that we wish to borrow this value, rather than move it. These two terms are explained fully later in later chapters.
+      let line_num = i + 1;
+      println!("{}: {}", line_num, line);
+    }
+  }
+}
-- 
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