Add docs and tests for switch.

doc/src/SUMMARY.md

@@ -117,13 +117,14 @@ The Rhai Scripting Language
    6. [Subtle Semantic Changes](engine/optimize/semantics.md)
 8. [Usage Patterns](patterns/index.md)
    1. [Object-Oriented Programming (OOP)](patterns/oop.md)
-   2. [Loadable Configuration](patterns/config.md)
-   3. [Control Layer](patterns/control.md)
-   4. [Singleton Command](patterns/singleton.md)
-   5. [Multi-Layer Functions](patterns/multi-layer.md)
-   6. [One Engine Instance Per Call](patterns/parallel.md)
-   7. [Scriptable Event Handler with State](patterns/events.md)
-   8. [Dynamic Constants Provider](patterns/dynamic-const.md)
+   2. [Working With Rust Enums](patterns/enums.md)
+   3. [Loadable Configuration](patterns/config.md)
+   4. [Control Layer](patterns/control.md)
+   5. [Singleton Command](patterns/singleton.md)
+   6. [Multi-Layer Functions](patterns/multi-layer.md)
+   7. [One Engine Instance Per Call](patterns/parallel.md)
+   8. [Scriptable Event Handler with State](patterns/events.md)
+   9. [Dynamic Constants Provider](patterns/dynamic-const.md)
 9. [Advanced Topics](advanced.md)
    1. [Capture Scope for Function Call](language/fn-capture.md)
    2. [Low-Level API](rust/register-raw.md)

doc/src/language/switch.md

@@ -71,20 +71,25 @@ switch map {
 }
 ```
 
+Switching on [arrays] is very useful when working with Rust enums (see [this chapter]({{rootUrl}}/patterns/enums.md)
+for more details).
 
-Difference From If-Else Chain
------------------------------
 
-Although a `switch` expression looks _almost_ the same as an `if`-`else` chain,
+Difference From `if` - `else if` Chain
+-------------------------------------
+
+Although a `switch` expression looks _almost_ the same as an `if`-`else if` chain,
 there are subtle differences between the two.
 
+### Look-up Table vs `x == y`
+
 A `switch` expression matches through _hashing_ via a look-up table.
-Therefore, matching is very fast.  Walking down an `if`-`else` chain
-will be _much_ slower.
+Therefore, matching is very fast.  Walking down an `if`-`else if` chain
+is _much_ slower.
 
 On the other hand, operators can be [overloaded][operator overloading] in Rhai,
 meaning that it is possible to override the `==` operator for integers such
-that `if x == y` returns a different result from the built-in default.
+that `x == y` returns a different result from the built-in default.
 
 `switch` expressions do _not_ use the `==` operator for comparison;
 instead, they _hash_ the data values and jump directly to the correct
@@ -95,3 +100,12 @@ the `==` operator will have no effect.
 Therefore, in environments where it is desirable to [overload][operator overloading]
 the `==` operator - though it is difficult to think of valid scenarios where you'd want
 `1 == 1` to return something other than `true` - avoid using the `switch` expression.
+
+### Efficiency
+
+Because the `switch` expression works through a look-up table, it is very efficient
+even for _large_ number of cases; in fact, switching is an O(1) operation regardless
+of the size of the data and number of cases to match.
+
+A long `if`-`else if` chain becomes increasingly slower with each additional case
+because essentially an O(n) _linear scan_ is performed.

doc/src/patterns/enums.md

@@ -0,0 +1,64 @@
+Working With Rust Enums
+=======================
+
+{{#include ../links.md}}
+
+Enums in Rust are typically used with _pattern matching_.  Rhai is dynamic, so although
+it integrates with Rust enum variants just fine (treated transparently as [custom types]),
+it is impossible (short of registering a complete API) to distinguish between individual
+enum variants or to extract internal data from them.
+
+
+Switch Through Arrays
+---------------------
+
+An easy way to work with Rust enums is through exposing the internal data of each enum variant
+as an [array], usually with the name of the variant as the first item:
+
+```rust
+use rhai::{Engine, Array};
+
+#[derive(Debug, Clone)]
+enum MyEnum {
+    Foo,
+    Bar(i64),
+    Baz(String, bool)
+}
+
+impl MyEnum {
+    fn get_enum_data(&mut self) -> Array {
+        match self {
+            Self::Foo => vec![
+                "Foo".into()
+            ] as Array,
+            Self::Bar(num) => vec![
+                "Bar".into(), (*num).into()
+            ] as Array,
+            Self::Baz(name, option) => vec![
+                "Baz".into(), name.clone().into(), (*option).into()
+            ] as Array
+        }
+    }
+}
+
+engine
+    .register_type_with_name::<MyEnum>("MyEnum")
+    .register_get("enum_data", MyEnum::get_enum_data);
+```
+
+Then it is a simple matter to match an enum via the `switch` expression:
+
+```c
+// Assume 'value' = 'MyEnum::Baz("hello", true)'
+// 'get_data' creates a variable-length array with 'MyEnum' data
+let x = switch value.enum_data {
+    ["Foo"] => 1,
+    ["Bar", 42] => 2,
+    ["Bar", 123] => 3,
+    ["Baz", "hello", false] => 4,
+    ["Baz", "hello", true] => 5,
+    _ => 9
+};
+
+x == 5;
+```

doc/src/rust/custom.md

@@ -191,3 +191,10 @@ engine.register_fn("==",
 let item = new_ts();        // construct a new 'TestStruct'
 item in array;              // 'in' operator uses '=='
 ```
+
+
+Working With Enums
+------------------
+
+It is quite easy to use Rust enums with Rhai.
+See [this chapter]({{rootUrl}}/patterns/enums.md) for more details.

tests/switch.rs

@@ -1,4 +1,4 @@
-use rhai::{Engine, EvalAltResult, Scope, INT};
+use rhai::{Dynamic, Engine, EvalAltResult, Scope, INT};
 
 #[test]
 fn test_switch() -> Result<(), Box<EvalAltResult>> {
@@ -62,3 +62,58 @@ fn test_switch() -> Result<(), Box<EvalAltResult>> {
 
     Ok(())
 }
+
+#[cfg(not(feature = "no_index"))]
+mod test_switch_enum {
+    use super::*;
+    use rhai::Array;
+    #[derive(Debug, Clone)]
+    enum MyEnum {
+        Foo,
+        Bar(i64),
+        Baz(String, bool),
+    }
+
+    impl MyEnum {
+        fn get_enum_data(&mut self) -> Array {
+            match self {
+                Self::Foo => vec!["Foo".into()] as Array,
+                Self::Bar(num) => vec!["Bar".into(), (*num).into()] as Array,
+                Self::Baz(name, option) => {
+                    vec!["Baz".into(), name.clone().into(), (*option).into()] as Array
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_switch_enum() -> Result<(), Box<EvalAltResult>> {
+        let mut engine = Engine::new();
+
+        engine
+            .register_type_with_name::<MyEnum>("MyEnum")
+            .register_get("get_data", MyEnum::get_enum_data);
+
+        let mut scope = Scope::new();
+        scope.push("x", MyEnum::Baz("hello".to_string(), true));
+
+        assert_eq!(
+            engine.eval_with_scope::<INT>(
+                &mut scope,
+                r#"
+                    switch x.get_data {
+                        ["Foo"] => 1,
+                        ["Bar", 42] => 2,
+                        ["Bar", 123] => 3,
+                        ["Baz", "hello", false] => 4,
+                        ["Baz", "hello", true] => 5,
+                        _ => 9
+                    }
+                "#
+            )?,
+            5
+        );
+
+        Ok(())
+    }
+}