Get icon paths using an overridable method

eu.fbk.tools.editor/eu.fbk.tools.editor.contract.expression.ui/src/eu/fbk/tools/editor/contract/expression/ui/contentassist/ExpressionProposalProvider.xtend

@@ -21,17 +21,20 @@ import eu.fbk.tools.editor.contract.expression.validation.DefineProposalProvider
  * on how to customize the content assistant.
  */
 class ExpressionProposalProvider extends AbstractExpressionProposalProvider {
+	val protected INPUT_PATH = "/resources/icons/input_port.png"
+	val protected OUTPUT_PATH = "/resources/icons/output_port.png"
+	val protected INOUT_PATH = "/resources/icons/input_output_port.png"
 	val images = new Hashtable<PortProposalProvider.PortDirection, Image>()
 
 	override complete_PortId(EObject model, RuleCall ruleCall,
 		org.eclipse.xtext.ui.editor.contentassist.ContentAssistContext context, ICompletionProposalAcceptor acceptor) {
 		if (images.empty) {
 			val inPortImageDescriptor = ExpressionActivator.imageDescriptorFromPlugin(
-				"eu.fbk.tools.editor.contract.expression.ui", "/resources/icons/input_port.png");
+				"eu.fbk.tools.editor.contract.expression.ui", getInputPath);
 			val outPortImageDescriptor = ExpressionActivator.imageDescriptorFromPlugin(
-				"eu.fbk.tools.editor.contract.expression.ui", "/resources/icons/output_port.png");
+				"eu.fbk.tools.editor.contract.expression.ui", getOutputPath);
 			val inoutPortImageDescriptor = ExpressionActivator.imageDescriptorFromPlugin(
-				"eu.fbk.tools.editor.contract.expression.ui", "/resources/icons/input_output_port.png");
+				"eu.fbk.tools.editor.contract.expression.ui", getInOutPath);
 
 			images.put(PortProposalProvider.PortDirection.IN, inPortImageDescriptor.createImage());
 			images.put(PortProposalProvider.PortDirection.OUT, outPortImageDescriptor.createImage());
@@ -75,6 +78,18 @@ class ExpressionProposalProvider extends AbstractExpressionProposalProvider {
 		super.complete_PortId(model, ruleCall, context, acceptor)
 	}
 
+	def String getInputPath() {
+		return INPUT_PATH
+	}
+
+	def String getOutputPath() {
+		return OUTPUT_PATH
+	}
+
+	def String getInOutPath() {
+		return INOUT_PATH
+	}
+
 	override complete_ParameterId(EObject model, RuleCall ruleCall,
 		org.eclipse.xtext.ui.editor.contentassist.ContentAssistContext context, ICompletionProposalAcceptor acceptor) {
 		val defaultPriority = getPriorityHelper().getDefaultPriority();