Macro variant_params 

macro_rules! variant_params {
    () => { ... };
    ($($T:ident),+) => { ... };
}

Compose a Problem::variant() body from type parameter names.

All variant dimensions must be types implementing VariantParam.

Usage

variant_params![]           // -> vec![]
variant_params![G, W]       // -> vec![(G::CATEGORY, G::VALUE), ...]