Compiler modes and strictness

PXX has one dialect, not several semantic modes. What changes is how strict that dialect is about a handful of FPC-parity rules. This page explains the model as a whole; the individual switches are listed on the command line page and, for the in-source forms, on the directives page.

The model: lax → strict → mimic

• Lax by default. PXX's own dialect is deliberately permissive. Declaration order, member visibility, operator and overload resolution, and case-label checking are all relaxed unless you ask for the stricter behavior. This keeps quick programs and in-progress code compiling without ceremony.

• --strict — the umbrella. Turns on the FPC-parity strictness family together. Today that family is the routine-visibility check (--require-forward); the umbrella name is the stable entry point as more checks join it.

• Granular switches — one rule at a time. Each check is independently toggleable, so you can tighten (or loosen) exactly one rule without the whole umbrella:

  Switch	What it enforces	Lax default
  --require-forward	Routine defined/declared before its call site.	Whole-source pre-scan finds it anywhere.
  --strict-overload	Explicit overload; on overloaded routines.	Marker not required.
  --strict-operator	Reject = / <> on class operands.	Value-equality operators allowed.
  --strict-case	Inverted-range and duplicate/overlapping case labels are errors.	First-match, no diagnostics.
  --strict-visibility	private / protected / strict access is enforced.	Markers parsed, access granted anywhere.
  --lax-decl-order	(opt-out) declare-before-use for forward-visible globals.	Enforced by default.

  Each also has an in-source directive form ({$STRICT_OVERLOAD ON}, {$STRICT_CASE ON}, {$DECLORDER OFF}, …) so a source file can carry its own strictness need — see directives.

• --strict-fpc — the FPC-parity umbrella. Turns on the strict checks that match FPC's behaviour and are proven to compile the real FPC corpora at once: --strict-case, --strict-operator, --strict-visibility, and --require-forward. In-source form: {$STRICT_FPC ON}.

  --strict-overload is not part of the umbrella. PXX's own libraries overload freely without the overload; marker — that is the intended lax dialect — so requiring the marker would reject the very libraries FPC-oriented code links against. It remains available as a standalone switch for marker-clean code.

• --mimic-fpc — the compatibility preset. For compiling FPC-oriented code. It is --strict-fpc plus what makes PXX present as FPC: the curated FPC define set (so identity-probing headers pick their FPC path) and IO checking ({$I+}). A preset built on top of the strict family, not a separate mode. The in-source equivalent is {$MIMIC FPC}. For the FPC-specific details of what ports and what does not, see FPC compatibility.

Why lax is the default

PXX is its own dialect first and an FPC-compatibility tool second. The lax default serves the dialect; the strict flags and --mimic-fpc serve compatibility when you want it. That split is deliberate: you opt into FPC-parity strictness per rule, rather than opting out of it.

Note that {$mode objfpc} / -Mobjfpc and the other FPC mode markers are accepted as compatibility markers only — they do not switch PXX into a different semantic mode. Strictness is controlled by the switches above, not by the mode marker.

Next

• Command line
• Compiler directives
• FPC compatibility