refactor: Replace circuit.queue with iterator

qibo-core-py/examples/circuit.py

@@ -18,4 +18,4 @@
 backend = NumpyBackend()
 result = backend.execute_circuit(c)
 print()
-print(result)
+print(result)

qibo-core-py/qibo_core/numpy.py

@@ -430,7 +430,7 @@ def execute_circuit(self, circuit, initial_state=None, nshots=1000):
                     # cast to proper complex type
                     state = self.cast(initial_state)
 
-                for gate in circuit.queue:
+                for gate, targets in circuit:
                     state = gate.apply_density_matrix(self, state, nqubits)
 
             else:
@@ -440,7 +440,7 @@ def execute_circuit(self, circuit, initial_state=None, nshots=1000):
                     # cast to proper complex type
                     state = self.cast(initial_state)
 
-                for gate, targets in zip(*circuit.queue):
+                for gate, targets in circuit:
                     # TODO: Handle measurements and ``CallbackGate``
                     state = self.apply_gate(gate, targets, state, nqubits)
 

qibo-core-py/src/circuit.rs

@@ -9,13 +9,13 @@ pub mod circuit {
     use super::*;
 
     #[pyclass]
-    struct Circuit(prelude::Circuit);
+    struct Circuit(prelude::Circuit, usize);
 
     #[pymethods]
     impl Circuit {
         #[new]
         fn new(elements: usize) -> Self {
-            Self(prelude::Circuit::new(elements))
+            Self(prelude::Circuit::new(elements), 0)
         }
 
         fn add(&mut self, gate: Gate, elements: Vec<usize>) {
@@ -32,14 +32,21 @@ pub mod circuit {
             vec![]
         }
 
-        #[getter]
-        fn queue(&self) -> (Vec<Gate>, Vec<Vec<usize>>) {
-            let queue = self.0.queue();
-            let mut pygates = vec![];
-            for &gate in queue.0.iter() {
-                pygates.push(Gate::to_python(gate));
+        fn __iter__(mut slf: PyRefMut<Self>) -> PyRefMut<Self> {
+            slf.1 = 0;
+            slf
+        }
+
+        fn __next__(mut slf: PyRefMut<Self>) -> Option<(Gate, Vec<usize>)> {
+            let gid = slf.1;
+            if gid < slf.0.n_gates() {
+                let gate = Gate::to_python(slf.0.gates(gid));
+                let targets = slf.0.elements(gid);
+                slf.1 += 1;
+                Some((gate, targets))
+            } else {
+                None
             }
-            (pygates, queue.1)
         }
 
         fn __str__(&self) -> String {

src/circuit.rs

@@ -92,10 +92,16 @@ impl Circuit {
         wire.into_iter().rev().collect()
     }
 
+    // Total number of elements in the circuit
     pub fn n_elements(&self) -> usize {
         self.ends.len()
     }
 
+    // Total number of gates in the circuit
+    pub fn n_gates(&self) -> usize {
+        self.gates.len()
+    }
+
     pub fn wires(&self) -> Vec<Vec<Gate>> {
         (0..self.n_elements()).map(|i| self.wire(i)).collect()
     }
@@ -132,13 +138,9 @@ impl Circuit {
             .collect()
     }
 
-    /// List of (gate, targeted elements) in the order given by the user
-    pub fn queue(&self) -> (&Vec<Gate>, Vec<Vec<usize>>) {
-        let mut elements = vec![];
-        for gid in 0..self.gates.len() {
-            elements.push(self.elements(gid));
-        }
-        (&self.gates, elements)
+    /// Gate in given position
+    pub fn gates(&self, gid: usize) -> Gate {
+        self.gates[gid]
     }
 
     pub fn draw(&self) -> String {