Turn Composer into a struct

And rename `Arithmetization` to `Gate`.

Resolves #802

CHANGELOG.md

@@ -16,6 +16,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Improve InvalidCircuitSize error [#792]
 - Hide all modules except 'prelude' [#782]
+- Turn `Composer` trait into a struct [#802]
+- Rename `Arithmetization` to `Gate` [#802]
+
+### Removed
+
+- Remove `Builder` struct with introduction of `Composer` struct [#802]
 
 ## [0.18.0] - 2023-12-13
 
@@ -542,6 +548,7 @@ is necessary since `rkyv/validation` was required as a bound.
 - Proof system module.
 
 <!-- ISSUES -->
+[#802]: https://github.com/dusk-network/plonk/issues/802
 [#797]: https://github.com/dusk-network/plonk/issues/797
 [#796]: https://github.com/dusk-network/plonk/issues/796
 [#792]: https://github.com/dusk-network/plonk/issues/792

README.md

@@ -36,9 +36,7 @@ pub struct TestCircuit {
 }
 
 impl Circuit for TestCircuit {
-    fn circuit<C>(&self, composer: &mut C) -> Result<(), Error>
-    where
-        C: Composer,
+    fn circuit(&self, composer: &mut Composer) -> Result<(), Error>
     {
         let a = composer.append_witness(self.a);
         let b = composer.append_witness(self.b);

benches/plonk.rs

@@ -31,10 +31,7 @@ impl<const DEGREE: usize> Default for BenchCircuit<DEGREE> {
 }
 
 impl<const DEGREE: usize> Circuit for BenchCircuit<DEGREE> {
-    fn circuit<C>(&self, composer: &mut C) -> Result<(), Error>
-    where
-        C: Composer,
-    {
+    fn circuit(&self, composer: &mut Composer) -> Result<(), Error> {
         let w_a = composer.append_witness(self.a);
         let w_b = composer.append_witness(self.b);
         let w_x = composer.append_witness(self.x);
@@ -59,19 +56,19 @@ impl<const DEGREE: usize> Circuit for BenchCircuit<DEGREE> {
             composer.component_add_point(w_z, w_z);
             composer.append_logic_and::<128>(w_a, w_b);
             composer.append_logic_xor::<128>(w_a, w_b);
-            composer.component_boolean(C::ONE);
+            composer.component_boolean(Composer::ONE);
             composer.component_decomposition::<254>(w_a);
             composer.component_mul_generator(
                 w_y,
                 dusk_jubjub::GENERATOR_EXTENDED,
             )?;
             composer.component_mul_point(w_y, w_z);
             composer.component_range::<128>(w_a);
-            composer.component_select(C::ONE, w_a, w_b);
-            composer.component_select_identity(C::ONE, w_z);
-            composer.component_select_one(C::ONE, w_a);
-            composer.component_select_point(C::ONE, w_z, w_z);
-            composer.component_select_zero(C::ONE, w_a);
+            composer.component_select(Composer::ONE, w_a, w_b);
+            composer.component_select_identity(Composer::ONE, w_z);
+            composer.component_select_one(Composer::ONE, w_a);
+            composer.component_select_point(Composer::ONE, w_z, w_z);
+            composer.component_select_zero(Composer::ONE, w_a);
 
             diff = composer.constraints() - prev;
             prev = composer.constraints();