feat(wpcarro/rust): Include std::fmt::Display example

Gotta know how to `to_string` things

Change-Id: I259ef61ecaf6ae7fabe0b3d211706ba5f429b3a7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6057
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>
Tested-by: BuildkiteCI

users/wpcarro/scratch/rust/src/json/mod.rs

@@ -0,0 +1,81 @@
+use serde::{Deserialize, Serialize};
+use serde_json::{json, Value};
+
+// From the serde_json docs:
+//
+// > There are three common ways that you might find yourself needing to work
+// > with JSON data in Rust.
+// >
+// > 1. As text data. An unprocessed string of JSON data that you receive on an
+// >    HTTP endpoint, read from a file, or prepare to send to a remote server.
+// > 2. As an untyped or loosely typed representation. Maybe you want to check
+// >    that some JSON data is valid before passing it on, but without knowing
+// >    the structure of what it contains. Or you want to do very basic
+// >    manipulations like insert a key in a particular spot.
+// > 3. As a strongly typed Rust data structure. When you expect all or most of
+// >    your data to conform to a particular structure and want to get real work
+// >    done without JSON’s loosey-goosey nature tripping you up.
+//
+// So let's take a look at all three...
+
+////////////////////////////////////////////////////////////////////////////////
+// Types
+////////////////////////////////////////////////////////////////////////////////
+
+#[derive(Serialize, Deserialize, Debug)]
+struct Person {
+    fname: String,
+    lname: String,
+    age: u8,
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Functions
+////////////////////////////////////////////////////////////////////////////////
+
+// 1) Reading/writing from/to plain text.
+//    TL;DR:
+//    - read:  serde_json::from_str(data)
+//    - write: x.to_string()
+pub fn one() {
+    let data = json!({
+        "fname": "William",
+        "lname": "Carroll",
+        "age": 30,
+    })
+    .to_string();
+
+    println!("result: {:?}", data);
+}
+
+// 2) Parse into a loosely typed representation; mutate it; serialize it back.
+//    TL;DR:
+//    - read:  serde_json::from_str(data)
+//    - write: x.to_string()
+pub fn two() {
+    let data = r#"{"fname":"William","lname":"Carroll","age":30}"#;
+
+    let mut parsed: Value = serde_json::from_str(data).unwrap();
+    parsed["fname"] = json!("Norm");
+    parsed["lname"] = json!("Macdonald");
+    parsed["age"] = json!(61);
+
+    let result = parsed.to_string();
+    println!("result: {:?}", result);
+}
+
+// 3) Parse into a strongly typed structure.
+//    TL;DR:
+//    - read:  serde_json::from_str(data)
+//    - write: serde_json::to_string(x).unwrap()
+pub fn three() {
+    let data = r#"{"fname":"William","lname":"Carroll","age":30}"#;
+
+    let mut read: Person = serde_json::from_str(data).unwrap();
+    read.fname = "Norm".to_string();
+    read.lname = "Macdonald".to_string();
+    read.age = 61;
+
+    let write = serde_json::to_string(&read).unwrap();
+    println!("result: {:?}", write);
+}