Advanced Reference

Advanced features are useful when authoring reusable templates, package APIs, or large module families.

Meaning of new

new amends a contextual value. With explicit type information, it amends that type's default value. Without explicit type information, the contextual type decides what is being amended.

Let Expressions

let introduces a local binding inside an expression. Use it to keep derived values close to their use site.

Type Tests and Casts

is checks whether a value conforms to a type. Casts should be close to the boundary where an unknown value becomes known.

Lists, Sets, Maps, and Regex

The advanced reference distinguishes language-level object collections (Listing, Mapping, dynamic objects) from standard-library collection values such as List, Set, Map, and Regex.

Type Aliases and Annotations

Type aliases name reusable contracts. Annotations attach metadata that tools, renderers, and documentation generators can inspect.

Anonymous Functions

Anonymous functions are useful for callbacks, renderer converters, and compact predicates. Move them into named functions when behavior becomes shared.

Amending Null Values

Nullable values can be amended when the type context supplies a default. Keep that behavior explicit in templates because it can surprise readers.

When Generators

when generators conditionally include members inside object bodies.

For Generators

for generators create elements or entries from iterable values. They cannot create properties.

Spread Syntax

Spread syntax copies members from an iterable or object into an enclosing object. Nullable spread uses ...?value.

Member Predicates

Member Predicates use [[...]] to select members for amendment or replacement. They are most useful when elements do not have stable keys.

Receiver Keywords

this, outer, super, and module control name lookup across nested objects, amends chains, classes, and modules.

Glob Patterns

Glob patterns are used by globbed imports and reads. *, **, ?, character classes, and sub-patterns all affect which modules or resources enter the graph.

Doc Comments, Name Resolution, and Reserved Names

Doc comments feed documentation tools. Name resolution decides which member or binding an identifier refers to. Reserved keywords and blank identifiers should be treated as syntax tools, not ordinary names.