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Generators and rbx.h#

rbx refuses to build a problem when a generator depends on rbx.h. This page explains why and how to proceed if you really need to.

Why this is an error#

rbx.h exposes getVar<T>("NAME"), which reads the problem's variables — your constraints — at compile time. That is exactly what a validator wants. A generator is different: its job is to produce a fixed, reproducible testset.

If a generator reads a constraint through getVar, then changing that constraint silently changes every test the generator produces — with no edit to the generator and no warning. A test that used to stress N = 10^5 quietly becomes N = 10^6 (or shrinks), solutions that were once correctly judged may flip, and nothing in your diff hints at why.

Example#

// gen_max.cpp — DON'T: depends on a constraint
#include "rbx.h"
#include "testlib.h"

int main(int argc, char* argv[]) {
    registerGen(argc, argv, 1);
    int n = getVar<int>("MAX_N");   // <-- silent dependency on MAX_N
    println(n);
    return 0;
}

Bump MAX_N in problem.rbx.yml and this generator now emits a different test, invisibly. Instead, pass the size explicitly as a generator argument so the testset is pinned by your generator calls:

// gen_max.cpp — DO: size comes from the call
#include "testlib.h"

int main(int argc, char* argv[]) {
    registerGen(argc, argv, 1);
    int n = atoi(argv[1]);          // value is fixed by the generator call
    println(n);
    return 0;
}

# problem.rbx.yml — the size lives with the call, visible in your diff
generators:
  - name: "gen_max"
    path: "gen_max.cpp"
# ...
  - generator: { name: "gen_max", args: "100000" }

Escape hatches#

If you understand the trade-off and still want a generator to use rbx.h:

  • For a single generator, add the suppression directive after the include:
#include "rbx.h"  // rbx-header-linter: disable
  • For the whole package, remove rbx-header from the cpp language's linters list in your env.rbx.yml:
- name: "cpp"
  # ...
  linters: [testlib]   # rbx-header removed