Derive Clone for Constraint and ProblemVariables (#107)

Author: hlvlad

src/constraint.rs

@@ -5,6 +5,7 @@ use core::fmt::{Debug, Formatter};
 use std::ops::{Shl, Shr, Sub};
 
 /// A constraint represents a single (in)equality that must hold in the solution.
+#[derive(Clone)]
 pub struct Constraint {
     /// The expression that is constrained to be null or negative
     pub(crate) expression: Expression,

src/variable.rs

@@ -371,7 +371,7 @@ pub fn variable() -> VariableDefinition {
 /// Each problem has a unique type, which prevents using the variables
 /// from one problem inside an other one.
 /// Instances of this type should be created exclusively using the [crate::variables!] macro.
-#[derive(Default)]
+#[derive(Default, Clone)]
 pub struct ProblemVariables {
     variables: Vec<VariableDefinition>,
     initial_count: usize,