FA-43534 / Borrow checking / Member archive

Opaque type variance records only one of its captured lifetime parameters · case 04

Opaque type variance records only one of its captured lifetime parameters.

Member previewVariant 4 · 3 implementations · 12 checks per implementation

Case contract

Infer lifetime parameter variance in a toy type tree. Variance signs are +1 covariant, -1 contravariant, 0 invariant; repeated different signs join to invariant. var(name); ref(lifetime,type) covariant both; mut(lifetime,type) covariant lifetime invariant payload; fn(argument,result) flips argument; tuple(list) joins; cell(type) invariant; phantom(type) covariant; array(type,length) covariant; opaque(parameters) invariant for every listed parameter; unused(name) contributes nothing. Return parameter-to-sign map.

Why this case matters

A finite offline static-analysis model of ownership and borrowing; it does not execute the analyzed program.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
opaque	`{}`	`{"a": 0, "b": 0}`	Failed

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