Introduce ScalarTerm struct to support Add<Scalar> for ScalarVar and Add<GroupVar> for Term (#53)

Co-authored-by: Michele Orrù <[email protected]>

Author: nategraf

src/linear_relation/convert.rs

@@ -0,0 +1,142 @@
+use ff::Field;
+use group::Group;
+
+use super::{GroupVar, ScalarTerm, ScalarVar, Sum, Term, Weighted};
+
+impl<G> From<ScalarVar<G>> for ScalarTerm<G> {
+    fn from(value: ScalarVar<G>) -> Self {
+        Self::Var(value)
+    }
+}
+
+impl<G: Group> From<ScalarVar<G>> for Weighted<ScalarTerm<G>, G::Scalar> {
+    fn from(value: ScalarVar<G>) -> Self {
+        ScalarTerm::from(value).into()
+    }
+}
+
+impl<G: Group> From<Weighted<ScalarVar<G>, G::Scalar>> for Weighted<ScalarTerm<G>, G::Scalar> {
+    fn from(value: Weighted<ScalarVar<G>, G::Scalar>) -> Self {
+        Self {
+            term: value.term.into(),
+            weight: value.weight,
+        }
+    }
+}
+
+// NOTE: Rust does not accept an impl over From<G::Scalar>
+impl<T: Field + Into<G::Scalar>, G: Group> From<T> for Weighted<ScalarTerm<G>, G::Scalar> {
+    fn from(value: T) -> Self {
+        Self {
+            term: ScalarTerm::Unit,
+            weight: value.into(),
+        }
+    }
+}
+
+impl<G> From<(ScalarVar<G>, GroupVar<G>)> for Term<G> {
+    fn from((scalar, elem): (ScalarVar<G>, GroupVar<G>)) -> Self {
+        Self {
+            scalar: scalar.into(),
+            elem,
+        }
+    }
+}
+
+impl<G> From<(ScalarTerm<G>, GroupVar<G>)> for Term<G> {
+    fn from((scalar, elem): (ScalarTerm<G>, GroupVar<G>)) -> Self {
+        Self { scalar, elem }
+    }
+}
+
+impl<G> From<GroupVar<G>> for Term<G> {
+    fn from(value: GroupVar<G>) -> Self {
+        Term {
+            scalar: ScalarTerm::Unit,
+            elem: value,
+        }
+    }
+}
+
+impl<G: Group> From<(ScalarVar<G>, GroupVar<G>)> for Weighted<Term<G>, G::Scalar> {
+    fn from(pair: (ScalarVar<G>, GroupVar<G>)) -> Self {
+        Term::from(pair).into()
+    }
+}
+
+impl<G: Group> From<(ScalarTerm<G>, GroupVar<G>)> for Weighted<Term<G>, G::Scalar> {
+    fn from(pair: (ScalarTerm<G>, GroupVar<G>)) -> Self {
+        Term::from(pair).into()
+    }
+}
+
+impl<G: Group> From<GroupVar<G>> for Weighted<Term<G>, G::Scalar> {
+    fn from(value: GroupVar<G>) -> Self {
+        Term::from(value).into()
+    }
+}
+
+impl<G: Group> From<Weighted<GroupVar<G>, G::Scalar>> for Weighted<Term<G>, G::Scalar> {
+    fn from(value: Weighted<GroupVar<G>, G::Scalar>) -> Self {
+        Weighted {
+            term: value.term.into(),
+            weight: value.weight,
+        }
+    }
+}
+
+impl<T, F: Field> From<T> for Weighted<T, F> {
+    fn from(term: T) -> Self {
+        Self {
+            term,
+            weight: F::ONE,
+        }
+    }
+}
+
+// NOTE: This is implemented directly for each of the key types to avoid collision with the blanket
+// Into impl provided by the standard library.
+macro_rules! impl_from_for_sum {
+    ($($type:ty),+) => {
+        $(
+        impl<G: Group, T: Into<$type>> From<T> for Sum<$type> {
+            fn from(value: T) -> Self {
+                Sum(vec![value.into()])
+            }
+        }
+
+        impl<G: Group, T: Into<$type>> From<Vec<T>> for Sum<$type> {
+            fn from(terms: Vec<T>) -> Self {
+                Self::from_iter(terms)
+            }
+        }
+
+        impl<G: Group, T: Into<$type>, const N: usize> From<[T; N]> for Sum<$type> {
+            fn from(terms: [T; N]) -> Self {
+                Self::from_iter(terms)
+            }
+        }
+
+        impl<G: Group, T: Into<$type>> FromIterator<T> for Sum<$type> {
+            fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
+                Self(iter.into_iter().map(|x| x.into()).collect())
+            }
+        }
+        )+
+    };
+}
+
+impl_from_for_sum!(
+    ScalarVar<G>,
+    GroupVar<G>,
+    Term<G>,
+    Weighted<ScalarVar<G>, G::Scalar>,
+    Weighted<GroupVar<G>, G::Scalar>,
+    Weighted<Term<G>, G::Scalar>
+);
+
+impl<T, F: Field> From<Sum<T>> for Sum<Weighted<T, F>> {
+    fn from(sum: Sum<T>) -> Self {
+        Self(sum.0.into_iter().map(|x| x.into()).collect())
+    }
+}