make-load-form

(make-load-form object &optional environment)

The generic function the COMPILER consults when an object appears as a literal in code it is compiling. Its method returns a form that reconstructs the object, and that form replaces the object in the compiled program.

An object gets into code that way when a macro splices a live object into its own expansion — the standard reason a library needs this. CFFI does it in every defcfun whose argument or return type is a defcenum, and declares a method so the object survives compilation.

Like print-object there is no system method: the compile path routes only a type some method specializes on. A type no method covers is dumped as it always was, by writing out its slots, so a program that defines no make-load-form method compiles exactly as before. The two-value form is honored: a method may return a creation form and an init form, and the init form runs against the freshly created object.

The creation form is evaluated once per program run, not once per use, so a method whose form is expensive (parsing a foreign type, compiling a scanner) costs that work one time.

The method is what lets an object with a slot the compiler cannot write out — a hash table, a foreign pointer — reach a compiled program at all. Without one such a literal fails the compile with Cannot quote: ..., which is the signal that the type wants a method.

The interpreter never needs any of this — its literal IS the live object — so the method only changes what a compiled program does, and the two agree by construction.

Lite: an object reached only through a quoted ARRAY or a hash table inside a constant is not rebuilt (a quoted cons structure is). The creation form may not refer back to the object being created.