add a serde_json example

Author: uniphil

examples/json.rs

@@ -0,0 +1,40 @@
+#[cfg(feature = "with_serde")]
+fn main() {
+    let mut estimator =
+        cardinality_estimator::CardinalityEstimator::<usize, wyhash::WyHash, 8, 5>::new();
+
+    println!(
+        "serialized empty estimator (small): {}",
+        serde_json::to_string_pretty(&estimator).unwrap()
+    );
+
+    estimator.insert(&0);
+
+    println!(
+        "serialized with one insert (small): {}",
+        serde_json::to_string_pretty(&estimator).unwrap()
+    );
+
+    estimator.insert(&1);
+    estimator.insert(&2);
+
+    println!(
+        "serialized with three inserts (array): {}",
+        serde_json::to_string_pretty(&estimator).unwrap()
+    );
+
+    for i in 3..1000 {
+        estimator.insert(&i);
+    }
+
+    println!(
+        "serialized with many inserts (HLL): {}",
+        serde_json::to_string_pretty(&estimator).unwrap()
+    );
+}
+
+#[cfg(not(feature = "with_serde"))]
+fn main() -> Result<(), u32> {
+    eprintln!("this example requires --features with_serde");
+    Err(1)
+}