x

Focused utility traits and value types for MoonBit

copy

path

trait

moonbit

moon add totto2727/x@0.6.0

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Author

totto2727

Version

0.6.0

License

MIT

Repository

github.com/totto2727-org/x

Last updated

2 days ago

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README

#totto2727/x

Focused utility traits and value types for MoonBit.

Copy is provided by the totto2727/x/copy package.

Typed absolute and relative filesystem paths are provided by the totto2727/x/path package.

JSON conversion for moonbit-community/yaml is provided by the totto2727/x/yaml package. MoonBit does not allow a foreign trait to be implemented for a foreign type, so the package exposes an owned Yaml wrapper with standard FromJson and ToJson implementations. Construct @x_yaml.Yaml(upstream_value) before encoding and use the wrapper's public value field to recover the upstream value after decoding. JSON values are converted to equivalent flat YAML values; integer JSON number syntax becomes Yaml::Integer, while other numbers become Yaml::Real. YAML inf and nan reals abort ToJson conversion, and non-finite JSON numbers fail FromJson, because JSON cannot represent non-finite numbers.

JSON conversion for bobzhang/toml is provided by the totto2727/x/toml package through the same owned-wrapper pattern. Its TomlValue wrapper implements standard FromJson and ToJson and represents tables, arrays, strings, finite numbers, and booleans as their natural JSON equivalents. Construct @x_toml.TomlValue(upstream_value) before encoding and use the wrapper's public value field after decoding. TOML arrays may contain values of different types, matching TOML 1.0 and later. TOML date-time variants are flattened to their stored date strings. Converting those strings back from JSON produces TomlString, so date-time type information is intentionally not restored. JSON null is rejected because TOML has no corresponding value. TOML inf and nan floats abort ToJson conversion, and non-finite JSON numbers fail FromJson, because JSON cannot represent non-finite numbers.

JSON flattening is provided by totto2727/x/json. Both flatten and from_flatten_json require either RFC 6901 JsonPointer paths or JavaScript-style property and array-index paths. flatten expands arrays by default and accepts array_mode=Preserve to retain each array as a single Json leaf. Values remain Json; both operations reject paths over 16,384 UTF-16 code units or deeper than 256 segments, while reconstruction also rejects non-empty object-valued leaves, conflicting paths, and sparse arrays. A root empty object produces an empty flattened map, while nested empty objects are preserved as Json leaves, including at array positions. JSON Pointer rejects object keys matching RFC 6901 array-index syntax because they are indistinguishable from array indices without an existing document; use JavaScript bracket notation when those keys must round-trip.

MoonBit does not move values when they are passed to a function, so this package is not a marker for Rust-style move semantics. Copy::copy instead creates an independent logical copy. Composite implementations recursively copy their contents, while immutable storage may be shared when it cannot expose mutation.

Copy has no blanket or default implementation. Every custom type must explicitly define how its independent logical copy is constructed so mutable fields and collections cannot be shared accidentally.

#Generic copying

Use a Copy bound when an operation must produce a logically independent value:

fn[T : Copy] duplicate(value : T) -> (T, T) {
  (Copy::copy(value), Copy::copy(value))
}

test {
  debug_inspect(duplicate(42), content="(42, 42)")
}

The package implements Copy for primitive and immutable scalar values, Option, Result, Array, FixedArray, ReadOnlyArray, Map, and two- and three-element tuples. Composite implementations require their contained values to implement Copy; map keys must also implement Hash and Eq.

#Custom mutable values

Mutable types define their own copy policy:

struct Counter {
  mut value : Int
}

impl Copy for Counter with fn copy(self) {
  Counter::{ value: self.value }
}

test {
  let source = Counter::{ value: 1 }
  let copied = Copy::copy(source)
  copied.value = 2
  debug_inspect((source.value, copied.value), content="(1, 2)")
}

MoonBit's trait syntax and generic trait bounds are documented in the official Method and Trait reference.

#Typed paths

AbsolutePath and RelativePath normalize moonbitlang/x/path.Path values and validate their path form at construction. Their inner Path remains available through the public readonly path field.

let root = @typed_path.AbsolutePath(@path.Path("/workspace/./project"))
let source = @typed_path.RelativePath(@path.Path("src/../README.md"))
let readme = @typed_path.Path::join(root, source)
println(@typed_path.Path::to_string(readme))

Both types encode to a JSON string and decode through their validating constructors.

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