VISIT

VISIT is a statement for type-specializing code over the active payload of a VARIANT or INLINE_VARIANT. It does not accept unions or other value types.

Syntax

The five forms are:

VISIT variable;
VISIT expression AS name;
VISIT variable { statements }
VISIT expression AS name { statements }
VISIT EXTEND expression AS name;

Without AS, the subject must be one bare identifier. The identifier is also the payload binding and shadows the variant variable within the specialized region. With AS, name is the payload binding and the subject may be any expression. EXTEND is valid only in the final semicolon form.

The header AS is recognized only at the top level of the subject. An AS inside a cast, call, lambda, bracketed expression, comment, or nested braces is part of the expression rather than the VISIT header.

Specialized region

The semicolon forms specialize the lexical remainder of the current block. The attached-block forms specialize only their attached block. A continuation therefore consumes all following sibling statements in its block; nested continuations are interpreted inside-out.

The subject is evaluated exactly once. The compiler generates the specialized region once for every non-VOID alternative in declaration order, even when a particular compile-time execution already knows the active alternative. Nested visits multiply their specializations. Every generated specialization remains a lowering dependency.

Payload binding and qualification

Each specialization projects a reference to the active payload. The reference preserves the subject's usable qualifier: a mutable subject exposes a mutable payload, while a constant subject exposes only constant access. Mutating a mutable payload changes the object held by the variant.

An attached-block binding ends when its block joins and the outer lookup is restored. A continuation binding remains in force through the enclosing block's lexical remainder.

Temporary lifetime

The forms have three lifetime policies:

Form	Evaluation temporaries retained through the specialized region
VISIT variable;	The borrowed variable reference only
VISIT expression AS name;	The exact final temporary variant, when temporary, and its payload reference
VISIT variable { ... }	The borrowed variable reference only
VISIT expression AS name { ... }	Every temporary created while evaluating the expression
VISIT EXTEND expression AS name;	Every temporary created while evaluating the expression

The ordinary named continuation discards intermediate evaluation temporaries before dispatch. It does not copy or move the final variant to extend its lifetime. The attached named form and EXTEND dispatch from the complete post-evaluation state, so intermediate temporaries remain alive until the specialized region exits.

Normal lifetime cleanup applies on fallthrough, RETURN, BREAK, CONTINUE, and a valid GOTO out of the region.

VOID alternatives

If the variant declaration contains VOID, only the two attached-block forms are permitted. The VOID runtime path skips directly past the attached block. The compiler does not generate the block as a VOID specialization and does not create a payload binding for that path.

All three continuation forms are rejected for any variant whose declaration contains VOID, regardless of which alternative is active at a particular use.

Valueless state

Visiting a valueless variant is undefined behavior. The generated valueless dispatch path terminates as unreachable; it performs no cleanup and has no successor. Programs must test value?? or otherwise establish that an alternative is active before visiting a potentially valueless variant.

Generated identities and labels

Each alternative expansion has distinct internal identities for lambdas, static locals, and point labels. Point labels declared inside a visited region are remapped per specialization, including when visits are nested.

A GOTO within a specialization may exit to an outer point label when the ordinary lifetime-state rules permit that transition. A GOTO outside the visited region cannot enter an alternative-local point label.

MATCH provides distinct source blocks, guards, union option selection, and explicit valueless handling for alternatives.