Wrap captureCons and releaseCons

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 ### Added
+- Added `Model.captureCons()`, `Model.releaseCons()`, `Model.getConsNUses()`, `Model.captureVar()`, `Model.releaseVar()`, and `Model.getVarNUses()`
 ### Fixed
 ### Changed
 - Speed up `Expr.__add__` and `Expr.__iadd__` via the C-level API

src/pyscipopt/scip.pxd

@@ -820,6 +820,7 @@ cdef extern from "scip/scip.h":
     SCIP_RETCODE SCIPcaptureVar(SCIP* scip, SCIP_VAR* var)
     SCIP_RETCODE SCIPaddPricedVar(SCIP* scip, SCIP_VAR* var, SCIP_Real score)
     SCIP_RETCODE SCIPreleaseVar(SCIP* scip, SCIP_VAR** var)
+    int SCIPvarGetNUses(SCIP_VAR* var)
     SCIP_RETCODE SCIPtransformVar(SCIP* scip, SCIP_VAR* var, SCIP_VAR** transvar)
     SCIP_RETCODE SCIPgetTransformedVar(SCIP* scip, SCIP_VAR* var, SCIP_VAR** transvar)
     SCIP_RETCODE SCIPaddVarLocks(SCIP* scip, SCIP_VAR* var, int nlocksdown, int nlocksup)
@@ -913,6 +914,7 @@ cdef extern from "scip/scip.h":
     # Constraint Methods
     SCIP_RETCODE SCIPcaptureCons(SCIP* scip, SCIP_CONS* cons)
     SCIP_RETCODE SCIPreleaseCons(SCIP* scip, SCIP_CONS** cons)
+    int SCIPconsGetNUses(SCIP_CONS* cons)
     SCIP_RETCODE SCIPtransformCons(SCIP* scip, SCIP_CONS* cons, SCIP_CONS** transcons)
     SCIP_RETCODE SCIPgetTransformedCons(SCIP* scip, SCIP_CONS* cons, SCIP_CONS** transcons)
     SCIP_RETCODE SCIPgetConsVars(SCIP* scip, SCIP_CONS* cons, SCIP_VAR** vars, int varssize, SCIP_Bool* success)

src/pyscipopt/scip.pxi

@@ -4636,6 +4636,62 @@ cdef class Model:
         var.scip_var = NULL
         return deleted
 
+    def captureVar(self, Variable var):
+        """
+        Increase the usage counter of a variable. Must be matched by a releaseVar.
+
+        Parameters
+        ----------
+        var : Variable
+            variable to capture
+
+        """
+        PY_SCIP_CALL(SCIPcaptureVar(self._scip, var.scip_var))
+
+    def releaseVar(self, Variable var):
+        """
+        Decrease the usage counter of a variable.
+
+        Unlike the underlying ``SCIPreleaseVar``, this wrapper refuses to
+        release the last reference: it must be paired with a prior
+        captureVar call. This guarantees the variable is never freed via
+        this method and the wrapper's pointer stays valid.
+
+        Parameters
+        ----------
+        var : Variable
+            variable to release
+
+        Raises
+        ------
+        Exception
+            if releasing would free the variable (no matching captureVar).
+
+        """
+        cdef SCIP_VAR* scip_var = var.scip_var
+        if SCIPvarGetNUses(scip_var) <= 1:
+            raise Exception(
+                "releaseVar would free the variable; must be paired with "
+                "a prior captureVar call."
+            )
+        PY_SCIP_CALL(SCIPreleaseVar(self._scip, &scip_var))
+
+    def getVarNUses(self, Variable var):
+        """
+        Get the number of times the variable is currently captured.
+
+        Parameters
+        ----------
+        var : Variable
+            variable to query
+
+        Returns
+        -------
+        int
+
+        """
+        return SCIPvarGetNUses(var.scip_var)
+
     def aggregateVars(self, Variable varx, Variable vary, coefx=1.0, coefy=-1.0, rhs=0.0):
         """
         Aggregate two variables by adding an aggregation constraint.
@@ -8568,7 +8624,63 @@ cdef class Model:
 
         """
         PY_SCIP_CALL(SCIPdelConsLocal(self._scip, cons.scip_cons))
-
+
+    def captureCons(self, Constraint cons):
+        """
+        Increase the usage counter of a constraint. Must be matched by a releaseCons.
+
+        Parameters
+        ----------
+        cons : Constraint
+            constraint to capture
+
+        """
+        PY_SCIP_CALL(SCIPcaptureCons(self._scip, cons.scip_cons))
+
+    def releaseCons(self, Constraint cons):
+        """
+        Decrease the usage counter of a constraint.
+
+        Unlike the underlying ``SCIPreleaseCons``, this wrapper refuses to
+        release the last reference: it must be paired with a prior
+        captureCons call. This guarantees the constraint is never freed via
+        this method and the wrapper's pointer stays valid.
+
+        Parameters
+        ----------
+        cons : Constraint
+            constraint to release
+
+        Raises
+        ------
+        Exception
+            if releasing would free the constraint (no matching captureCons).
+
+        """
+        cdef SCIP_CONS* scip_cons = cons.scip_cons
+        if SCIPconsGetNUses(scip_cons) <= 1:
+            raise Exception(
+                "releaseCons would free the constraint; must be paired with "
+                "a prior captureCons call."
+            )
+        PY_SCIP_CALL(SCIPreleaseCons(self._scip, &scip_cons))
+
+    def getConsNUses(self, Constraint cons):
+        """
+        Get the number of times the constraint is currently captured.
+
+        Parameters
+        ----------
+        cons : Constraint
+            constraint to query
+
+        Returns
+        -------
+        int
+
+        """
+        return SCIPconsGetNUses(cons.scip_cons)
+
     def getValsLinear(self, Constraint cons):
         """
         Retrieve the coefficients of a linear constraint