48 lines
2.0 KiB
Markdown
48 lines
2.0 KiB
Markdown
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Parse an Object Map from JSON
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============================
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{{#include ../links.md}}
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The syntax for an [object map] is extremely similar to JSON, with the exception of `null` values which can
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technically be mapped to [`()`]. A valid JSON string does not start with a hash character `#` while a
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Rhai [object map] does - that's the major difference!
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Use the `Engine::parse_json` method to parse a piece of JSON into an object map:
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```rust
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// JSON string - notice that JSON property names are always quoted
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// notice also that comments are acceptable within the JSON string
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let json = r#"{
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"a": 1, // <- this is an integer number
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"b": true,
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"c": 123.0, // <- this is a floating-point number
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"$d e f!": "hello", // <- any text can be a property name
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"^^^!!!": [1,42,"999"], // <- value can be array or another hash
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"z": null // <- JSON 'null' value
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}
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"#;
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// Parse the JSON expression as an object map
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// Set the second boolean parameter to true in order to map 'null' to '()'
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let map = engine.parse_json(json, true)?;
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map.len() == 6; // 'map' contains all properties in the JSON string
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// Put the object map into a 'Scope'
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let mut scope = Scope::new();
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scope.push("map", map);
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let result = engine.eval_with_scope::<INT>(r#"map["^^^!!!"].len()"#)?;
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result == 3; // the object map is successfully used in the script
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```
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Representation of Numbers
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------------------------
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JSON numbers are all floating-point while Rhai supports integers (`INT`) and floating-point (`FLOAT`) if
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the [`no_float`] feature is not used. Most common generators of JSON data distinguish between
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integer and floating-point values by always serializing a floating-point number with a decimal point
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(i.e. `123.0` instead of `123` which is assumed to be an integer). This style can be used successfully
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with Rhai [object maps].
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