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_archive/rhai_engine/rhaibook/language/dynamic.md

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+Dynamic Values
+==============
+
+{{#include ../links.md}}
+
+A `Dynamic` value can be _any_ type, as long as it implements `Clone`.
+
+~~~admonish warning.small "`Send + Sync`"
+
+Under the [`sync`] feature, all types must also be `Send + Sync`.
+~~~
+
+```rust
+let x = 42;         // value is an integer
+
+x = 123.456;        // value is now a floating-point number
+
+x = "hello";        // value is now a string
+
+x = x.len > 0;      // value is now a boolean
+
+x = [x];            // value is now an array
+
+x = #{x: x};        // value is now an object map
+```
+
+
+Use `type_of()` to Get Value Type
+---------------------------------
+
+Because [`type_of()`] a `Dynamic` value returns the type of the actual value,
+it is usually used to perform type-specific actions based on the actual value's type.
+
+```js
+let mystery = get_some_dynamic_value();
+
+switch type_of(mystery) {
+    "()" => print("Hey, I got the unit () here!"),
+    "i64" => print("Hey, I got an integer here!"),
+    "f64" => print("Hey, I got a float here!"),
+    "decimal" => print("Hey, I got a decimal here!"),
+    "range" => print("Hey, I got an exclusive range here!"),
+    "range=" => print("Hey, I got an inclusive range here!"),
+    "string" => print("Hey, I got a string here!"),
+    "bool" => print("Hey, I got a boolean here!"),
+    "array" => print("Hey, I got an array here!"),
+    "blob" => print("Hey, I got a BLOB here!"),
+    "map" => print("Hey, I got an object map here!"),
+    "Fn" => print("Hey, I got a function pointer here!"),
+    "timestamp" => print("Hey, I got a time-stamp here!"),
+    "TestStruct" => print("Hey, I got the TestStruct custom type here!"),
+    _ => print(`I don't know what this is: ${type_of(mystery)}`)
+}
+```
+
+
+Parse from JSON
+---------------
+
+~~~admonish warning.side "Requires `metadata`"
+
+`parse_json` is defined in the [`LanguageCorePackage`][built-in packages], which is excluded when using a [raw `Engine`].
+
+It also requires the [`metadata`] feature; the [`no_index`] and [`no_object`] features must _not_ be set.
+~~~
+
+Use `parse_json` to parse a JSON string into a [`Dynamic`] value.
+
+|           JSON type           |  Rhai type   |
+| :---------------------------: | :----------: |
+|  `number` (no decimal point)  |    `INT`     |
+| `number` (with decimal point) |   `FLOAT`    |
+|           `string`            |   [string]   |
+|           `boolean`           |    `bool`    |
+|            `Array`            |   [array]    |
+|           `Object`            | [object map] |
+|            `null`             |    [`()`]    |