Struct UnimplementedBackend 

pub struct UnimplementedBackend {
    pub backend: &'static str,
    pub family: &'static str,
    pub options: &'static [&'static str],
}

One linear-solver backend pounce does not implement, and the registered options that tune it.

Separate from UnimplementedFeature because the disposition is different: these warn and solve, they never refuse. See “Backend knobs warn, they do not refuse” in the module header for why.

Fields

backend: &'static str

Named in the warning, e.g. “the HSL MA97 sparse symmetric linear solver”.

family: &'static str

The registered prefix the family shares, quoted in the warning so the user learns the whole group is inert, not just the one option they happened to set.

options: &'static [&'static str]

Every registered option of this backend. Complete per family — backend_families_are_complete fails if the registry grows one that is missing here, which would hand it back its silence.