fieldIsVirtual (schema ordinal -- hasNoStorage)

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.

fieldIsVirtual (schema ordinal -- hasNoStorage)

Inputs

schema: Value or Ref whose dereferenced schema is Struct and whose selected item is tested.

ordinal: Zero-based item ordinal being tested.

Outputs

hasNoStorage: Known Cond result that is TRUE when the selected item has no runtime field storage.

fieldIsVirtual is a selected-item storage predicate. It tests whether one selected item of the dereferenced Struct schema has no runtime field storage.

TRUE includes static items and Meta items. Current field contents do not participate. This is a schema predicate, not a read-result predicate, so a static item can make fieldIsVirtual return TRUE even though reading that item later produces a non-Meta value and virtual? returns FALSE. A static Ref-like item can make both fieldIsVirtual and fieldIsRef return TRUE, because storage kind and schema kind are tested separately.

Behavior

The result is always known.

ordinal is a zero-based known Int32 selected-item ordinal.

TRUE means that the selected item has no runtime field storage.

Static items and Meta items report TRUE.

A static Ref-like item can make both fieldIsVirtual and fieldIsRef report TRUE.

Items with runtime field storage report FALSE.

The result depends only on the selected item storage kind, not on the item name or current field contents.

If ordinal is out of bounds for the Struct schema, the builtin raises a compilation error.

Example

{} 0 {} [ dict: { ordinaryField: 0; staticField: 0 virtual; staticCodeField: {} () {} codeRef virtual; metaField: (); }; "-- In-place field schema versus read result --" printCompilerMessage dict 0 fieldIsVirtual printStack _:; @dict 0 fieldRead virtual? printStack _:; "-- static field schema versus read result --" printCompilerMessage dict 1 fieldIsVirtual printStack _:; @dict 1 fieldRead virtual? printStack _:; "-- static Ref-like field schema versus read result --" printCompilerMessage dict 2 fieldIsVirtual printStack _:; dict 2 fieldIsRef printStack _:; @dict 2 fieldRead virtual? printStack _:; "-- meta field schema versus read result --" printCompilerMessage dict 3 fieldIsVirtual printStack _:; @dict 3 fieldRead virtual? printStack _:; tuple: (0 ()); "-- Tuple item storage --" printCompilerMessage tuple 0 fieldIsVirtual printStack _:; tuple 1 fieldIsVirtual printStack _:; 0 ] "main" exportFunction

Expected Output During Compilation

-- In-place field schema versus read result -- FALSE FALSE -- static field schema versus read result -- TRUE FALSE -- static Ref-like field schema versus read result -- TRUE TRUE FALSE -- meta field schema versus read result -- TRUE TRUE -- Tuple item storage -- FALSE TRUE