Element kinds

Every Element is one of the following kinds. The kind is the high 6 bits of the ElementId ; see the layout chapter. Trivial-kind Elements have no payload; payload-bearing kinds carry a &'static SomeInfo reference into the matching arena.

This is reference material, organised by family.

Trivial kinds (no payload)

Kind	Prelude constant	Denotes
`Null`	`NULL`	The value `null`.
`Never`	`NEVER`	The empty type ($\bot$).
`Void`	`VOID`	The PHP `void` (absence of return value).
`Placeholder`	`PLACEHOLDER`	Inference-time hole.
`Bool`	`BOOL`	`true` or `false`.
`True`	`TRUE`	The value `true`.
`False`	`FALSE`	The value `false`.
`Scalar`	`SCALAR`	`bool \| int \| float \| string`.
`Numeric`	`NUMERIC`	`int \| float \| numeric-string`.
`ArrayKey`	`ARRAY_KEY`	`int \| string`.
`ObjectAny`	`OBJECT_ANY`	Any object, no class commitment.
`Mixed`	`MIXED` (vanilla)	Universe top ($\top$), with optional axes via `MixedInfo`.

Mixed is technically payload-bearing (the MixedInfo carries the four axes), but the vanilla form (all axes default) is exposed as a constant and behaves trivially.

Scalar payload kinds

Kind	Payload	Denotes
`Int`	`IntInfo`	Integer (Unspecified, UnspecifiedLiteral, Literal(n), Range(IntRange)).
`Float`	`FloatInfo`	Float (Unspecified, Literal, NonZero).
`String`	`StringInfo`	String with literal slot + refinement flags.
`ClassLikeString`	`ClassLikeStringInfo`	A string naming a class-like (kind + specifier).

See scalars and class-like strings.

Object family

Kind	Payload	Denotes
`Object`	`ObjectInfo`	Named class (with optional type args, intersections, modality flags).
`Enum`	`EnumInfo`	Enum (with optional case).
`ObjectShape`	`ObjectShapeInfo`	Structural object type (with known properties, sealed/unsealed).
`HasMethod`	`HasMethodInfo`	Anything declaring a method named `m`.
`HasProperty`	`HasPropertyInfo`	Anything declaring a property named `p`.

See objects.

Collection family

Kind	Payload	Denotes
`Array`	`KeyedArrayInfo`	Keyed array (generic, sealed shape, or empty).
`List`	`ListInfo`	Int-keyed list (generic or sealed).
`Iterable`	`IterableInfo`	`iterable<K, V>`.

See arrays and iterables and callables.

Resource

Kind	Payload	Denotes
`Resource`	`ResourceInfo`	PHP resource (open / closed, named kind).

See resources.

Callable

Kind	Payload	Denotes
`Callable`	`CallableInfo`	Bare, signature, or closure form.

See iterables and callables.

Wrappers

Kind	Payload	Denotes
`Negated`	`NegatedInfo`	Set complement: `!T`.
`Intersected`	`IntersectedInfo`	Head + conjunct list: `H & C1 & ... & Cn`.

See wrappers.

Generics

Kind	Payload	Denotes
`GenericParameter`	`GenericParameterInfo`	Free template parameter (`T`).

See templates.

Unresolved

Kind	Payload	Denotes
`Alias`	`AliasInfo`	Type alias (resolved via `World::resolve_alias`).
`Reference`	`SymbolReference`	Name reference (class, alias, parameter, etc.).
`MemberReference`	`MemberReference`	Class-member type (`Foo::T`).
`GlobalReference`	`GlobalReference`	Global type variable.
`Conditional`	`ConditionalInfo`	`T extends U ? X : Y`.
`Derived`	`DerivedInfo`	`KeyOf<T>`, `ValueOf<T>`, `IndexAccess<T, K>`, etc.
`Variable`	`VariableInfo`	Analyser-introduced inference placeholder.

See unresolved elements and expand.

How to enumerate

use suffete::ElementKind;

// Every variant in declaration order.
for k in ElementKind::iter() {
    println!("{:?}", k);
}

The total count of variants is the size of core::mem::variant_count::<ElementKind>(). The maximum tag value is one less than the count.

Constructing each kind

For trivial kinds, use the prelude constants. For payload-bearing kinds, use the ElementId constructors when available, or interner().intern_* directly:

use suffete::{ElementId, prelude::INT};
use suffete::interner::interner;
use suffete::element::payload::*;
use mago_atom::atom;

// Trivial.
let _ = suffete::prelude::NULL;
let _ = INT;

// Convenience constructors.
let _ = ElementId::int_literal(7);
let _ = ElementId::string_literal("hello");
let _ = ElementId::named_object(atom("Foo"));
let _ = ElementId::named_object_with_args(atom("Box"), &[suffete::prelude::TYPE_INT]);
let _ = ElementId::enum_case(atom("Status"), atom("Active"));

// Direct interner.
let info = ResourceInfo { state: ResourceState::Open, kind: Some(atom("curl")) };
let _ = interner().intern_resource(info);

The full list of constructors is in src/element/id.rs; the per-kind interner methods are generated by the element_arena_methods! macro in src/interner/store.rs.

See also: Elements: the indivisible types for the conceptual overview; The ElementId tag layout for the bit layout; Prelude constants for the full prelude.

The Suffete Book