JustDummies

Any.OneOf draws one value from a pool of values. Handed generators, it infers the builder type as the pool’s element type: the pool holds recipes, and drawing from it yields a recipe rather than a value — which then flows on into the object and text positions JD005 and JD011 report.

What makes this a trap rather than an obvious slip is that the surface is inconsistent about it. Any.OneOf(Any.Int32(), Any.Int64()) fails type inference and the compiler stops you; Any.OneOf(Any.Int32(), Any.Int32()) binds cleanly and says nothing.

Noncompliant

IAny<AnyInt32> pool = Any.OneOf(Any.Int32().Positive(), Any.Int32().Negative());   // JD012
AnyInt32 drawn = pool.Generate();   // a recipe, not a number

Compliant

IAny<int> pool = Any.OneOf(Any.Int32().Positive().Generate(), Any.Int32().Negative().Generate());
int drawn = pool.Generate();

Note what the compliant form changes: the pool is built eagerly, one draw per element at construction, and Generate() then chooses among those fixed values. That is the documented semantics of a choice pool — if you wanted a fresh draw from a chosen generator on every call, that is a different intent and Any.OneOf is not the tool.

What it does not flag

• A pool of ordinary values, or of generated values.
• A OneOf on any type other than Any / AnyContext.
• A pool whose generators have different types — the compiler already refuses it.