The new FlowVariable API has some great features, but I would like to make a suggestion, which is probably only relevant in a small number of cases where the VariableType is not known until either in the code, e.g. an abstract NodeModel implementation which implementations will add a variable but the type will be determined in the subclass.
It is good practice in the NodeModel#configure() method to push place-holder variables with default values, so that downstream nodes know that the variable will exist.
In the legacy API, this was achieved with:
pushFlowVariableDouble("A double", 0.0);
pushFlowVariableInt("An int", 0);
pushFlowVariableString("A String", "");
The new API makes this more flexible, via the method pushFlowVariable(String name, VariableType<T> type, T value), but if we don’t know T then a default value is difficult to come by generically. As a simple example:
public abstract class MyNodeModel<T> extends NodeModel {
....
public DataTableSpec[] configure(DataTableSpec[] inSpecs) {
// Do some configure stuff
// ...
// Push a default value
pushFlowVariable("My Variable", getType(), getDefaultValue());
}
/** @return the variable type */
public abstract VariableType<T> getType();
/** @return the default value *?
public abstract T getDefaultValue();
}
Well, that’s OK, but VariableType already knows it’s default value -
for example, booleans default to false…
Making this method public would allow a much simpler #configure method in the above snippet:
// Push a default value
pushFlowVariable("My Variable", getType(), getType().defaultValue().get());
Actually, there are some alternative workarounds too, all of which might have their uses:
- In
NodeModel,pushFlowVariable(String name, VariableType<T> type, T value)does a few sanity checks and then callspushFlowVariable(new FlowVariable(name, type, value));This latter method is package private - making it protected visibility would mean thatpushFlowVariable(new FlowVariable("My Variable", getType()));was an alternative route to default as the 2-argumentFlowVariableconstructor creates a variable with the default value - In
NodeModel, a new methodpushFlowVariable(String name, VariableType<T> type)which pushed the variable onto the stack with the default value
Of course, there is an alternative workaround at the moment…
T defaultValue = new FlowVariable("My Variable", getType()).getValue(getType());
But that does feel a bit… convoluted! (Rather like this post has become - sorry!)
Steve