isConst (object -- isConst)

Inputs

• object: Current stack view whose immutability is tested.

Outputs

• isConst: Known Cond result that is TRUE when the current stack view is immutable.

It tests only the current stack view. The result depends on the object on the stack, not on whether the same underlying storage is also reachable through another Ref with different mutability. The view-changing builtins const and unconst can therefore change this result only for Ref inputs.

Behavior

• Immutable Ref views report TRUE.
• Mutable Ref views report FALSE.
• Text objects report TRUE, regardless of whether their contents are known at compile time.
• Code objects report TRUE, including known non-NIL, known NIL, and unknown Code objects.
• In-place objects, Block, and Meta objects report FALSE.
• NAME on a non-static, non-callable In-place local produces an immutable Ref view, while @NAME produces a mutable view; see selection.

Example

{} 0 {} [
  value: 7;
  codeLocal: {} () {} codeRef;
  unknownText: 0 ("") dynamic @; # an unknown Text
  [] !codeLocal # a non-NIL Code

  "-- mutable versus immutable Ref views --" printCompilerMessage
  @value isConst printStack _:;
  value isConst printStack _:;
  @value const isConst printStack _:;
  value unconst isConst printStack _:;

  "-- In-place values --" printCompilerMessage
  7 isConst printStack _:;
  0 dynamic isConst printStack _:;

  "-- Text and Code are const stack values --" printCompilerMessage
  "hi" isConst printStack _:;
  unknownText isConst printStack _:;
  {} () {} codeRef isConst printStack _:;
  {} () {} codeRef dynamic isConst printStack _:;
  @codeLocal isConst printStack _:;

  "-- Block and meta are not const stack values --" printCompilerMessage
  [] isConst printStack _:;
  () isConst printStack _:;

  0
] "main" exportFunction

Expected Output During Compilation

-- mutable versus immutable Ref views --
FALSE
TRUE
TRUE
FALSE
-- In-place values --
FALSE
FALSE
-- Text and Code are const stack values --
TRUE
TRUE
TRUE
TRUE
TRUE
-- Block and meta are not const stack values --
FALSE
FALSE

See also

• const builtin (object -- immutableView) Immutable view conversion for the current stack object.
• fieldIsRef builtin (schema ordinal -- isRefLike) Ref-like test for one selected item schema.
• isRef builtin (object -- object isRefLike) Current stack-object Ref-like test.
• managed? builtin (schema -- isManaged) Managed-lifetime schema test.
• unconst builtin (object -- mutableView) Mutable view conversion for the current stack object.