fieldIsRef (schema ordinal -- isRefLike)

Inputs

• schema: Object or Ref whose dereferenced schema is Struct and whose selected item is tested.
• ordinal: Zero-based item ordinal being tested.

Outputs

• isRefLike: Known Cond result that is TRUE when the selected item schema is Ref-like.

fieldIsRef is a selected-item schema predicate. It tests whether one selected item of the dereferenced Struct schema is Ref-like.

In this builtin, Ref-like means Ref, Code, or Text. Current field contents, current knownness, and current NIL status do not participate. This is a schema predicate, not a read-result predicate, so a non-static In-place item can make fieldIsRef return FALSE even though reading that item later produces a Ref-like result. A static Ref-like item can make both fieldIsRef and fieldIsVirtual return TRUE, because schema kind and runtime storage are tested separately.

Behavior

• ordinal is a zero-based known Int32 selected-item ordinal.
• All other item schemas, including In-place and Meta, report FALSE.
• If ordinal is out of bounds for the Struct schema, the builtin raises a compilation error.

Example

{} 0 {} [
  dict: {
    ordinaryField: 0;
    textField: 0 ("") dynamic @; # an unknown Text
    codeField: {} () {} codeRef;
    metaField: ();
  };

  "-- In-place field schema versus read result --" printCompilerMessage
  dict 0 fieldIsRef printStack _:;
  @dict 0 fieldRead isRef printStack _:; _:;

  "-- text field schema versus read result --" printCompilerMessage
  dict 1 fieldIsRef printStack _:;
  @dict 1 fieldRead isRef printStack _:; _:;

  "-- code field schema versus read result --" printCompilerMessage
  dict 2 fieldIsRef printStack _:;
  @dict 2 fieldRead isRef printStack _:; _:;

  "-- meta field schema versus read result --" printCompilerMessage
  dict 3 fieldIsRef printStack _:;
  @dict 3 fieldRead isRef printStack _:; _:;

  tuple: (0 "" {} () {} codeRef);
  "-- Tuple item schemas use the same category --" printCompilerMessage
  tuple 0 fieldIsRef printStack _:;
  tuple 1 fieldIsRef printStack _:;
  tuple 2 fieldIsRef printStack _:;

  0
] "main" exportFunction

Expected Output During Compilation

-- In-place field schema versus read result --
FALSE
0 Ref
TRUE
-- text field schema versus read result --
TRUE
Text
TRUE
-- code field schema versus read result --
TRUE
{} () {} codeRef CNIL
TRUE
-- meta field schema versus read result --
FALSE
()
FALSE
-- Tuple item schemas use the same category --
FALSE
TRUE
TRUE

See also

• @ builtin (ordinal structValue -- selectedItem) Ordinal-based one-item read with the ordinal before the Struct object.
• fieldRead builtin (structValue ordinal -- selectedItem) Ordinal-based one-item read with the Struct object before the ordinal.
• isRef builtin (object -- object isRefLike) Current stack object Ref-like predicate that preserves the object.
• fieldIsPrivate builtin (schema ordinal -- isPrivate) Visibility test for one selected Dict field.
• fieldIsVirtual builtin (schema ordinal -- hasNoStorage) No-storage test for one selected item.
• fieldCount builtin (schema -- itemCount) Item count of the Struct schema.
• fieldIndex builtin (schema itemName -- ordinal) Selected item ordinal from item name under last-match rules.
• fieldName builtin (schema ordinal -- itemName) Stored item name at one selected item ordinal.
• has builtin (schema itemName -- hasName) Schema-level known-name presence test.
• schemaName builtin (schema -- reportedName) Reported name of the dereferenced schema.