virtual? (schema -- isMeta)

Builtins

Name introduction, declaration modifiers, and module binding: NAME: ...;, codeRef, def, exportFunction, importFunction, importVariable, overload, private, static, use, and virtual.
Struct construction forms: (...), {...}, and array.
Selection forms: source-text selection with NAME and .NAME, read-only source-text selection with @NAME and .@NAME, and ordinal or known-name data-input selection with @, callField, and fieldRead.
Writing forms: source-text selection with !NAME and .!NAME, ordinal selection with ! and fieldWrite, and already-selected destination replacement with set.
Calling and control flow: call, if, loop, ucall, and uif.
Text operations: &, LF, attribute, textSize, and textSplit.
Condition constants, value comparison, and logical operators: <, =, >, DEBUG, FALSE, TRUE, and, is, lshift, or, rshift, xor, and ~.
Arithmetic and numeric transforms: *, +, -, /, ^, cast, ceil, cos, floor, log, log10, mod, neg, sin, and sqrt.
Reference, creation, and value-state operations: const, dynamic, isConst, isDirty, isDynamic, isRef, isStatic, known?, new, newVarOfTheSameType, stable?, unconst, and unknownStable?.
Schema and struct introspection: code?, codeRef?, fieldCount, fieldIndex, fieldIsRef, fieldIsVirtual, fieldName, has, isCombined, managed?, same, schemaName, and virtual?.
Storage and manual lifetime operations: addressToReference, alignment, manuallyDestroyVariable, manuallyInitVariable, storageAddress, and storageSize.
Diagnostics and compile-time failure: failCompilation, getCallTrace, printCompilerMessage, printStack, printStackTrace, and raiseStaticError.

virtual? (schema -- isMeta)

Inputs

schema: Value or Ref whose dereferenced schema is tested for Meta status.

Outputs

isMeta: Known Cond result that is TRUE when schema dereferences to Meta.

The name is historical. virtual? is a dereferenced-schema predicate. It tests whether the dereferenced schema is Meta.

It does not test whether a value or item was declared with virtual or whether a selected Struct item lacks runtime field storage. A static item can therefore make fieldIsVirtual return TRUE while a later read of that item makes virtual? return FALSE.

Ref inputs are followed before the test. Current value contents do not participate.

Behavior

The result is always known.

The result depends only on the dereferenced schema of schema.

TRUE means the schema is Meta.

The builtin does not test whether a field or local was declared with virtual.

fieldIsVirtual instead asks whether a selected Struct item lacks runtime field storage.

Known and unknown values of the same schema always produce the same result.

Example

{} 0 {} [ virtual staticLocal: 0; dict: { ordinaryField: 0; staticField: 0 virtual; metaField: (); }; "-- In-place field read result --" printCompilerMessage @dict 0 fieldRead virtual? printStack _:; dict 0 fieldIsVirtual printStack _:; "-- static field read result --" printCompilerMessage @dict 1 fieldRead virtual? printStack _:; dict 1 fieldIsVirtual printStack _:; "-- meta field read result --" printCompilerMessage @dict 2 fieldRead virtual? printStack _:; dict 2 fieldIsVirtual printStack _:; "-- value declared with virtual is still not meta --" printCompilerMessage staticLocal virtual? printStack _:; 0 ] "main" exportFunction

Expected Output During Compilation

-- In-place field read result -- FALSE FALSE -- static field read result -- FALSE TRUE -- meta field read result -- TRUE TRUE -- value declared with virtual is still not meta -- FALSE