Provide a default instance when creating a new ValueParameter

[abeham]

Adding a new ValueParameter<T> could create a default value if T is instantiable. For most ValueParameters you will want to have a value upon creation.

[mkommend]

r5843: Added code to create default values in ValueParameters if possible.

[mkommend]

r5848: Adapted TypeSelector to respect the new() constraint on generic types.

[mkommend]

r5859: Added version information to the plugin !treeNodes in the TypeSelector.

[mkommend]

r5898: Changed TypeSelector to display major and minor plugin version without brackets. IMHO it is not necessary to display the full version (this can be seen in the textbox below).

[abeham]

I was quite surprised recently when I saw this already in action. It's very handy when designing custom algorithms!

[abeham]

I tested this a little further and think that somewhere an error was introduced:

I tried to add a new parameter in a user-defined algorithm , e.g. a LookupParameter<T> and then choose the type for T. The dialog that lists all possible types for T however lists only instantiable types. A LookupParameter can look up a wide range of possible types, sometimes only specified by an interface. I think it should be and has been possible to create that parameter with IOperator as its generic type. The restriction to limit the type selector dialog to instantiable types should only be set if the generic type of a FixedValueParameter<T> is going to be defined. Maybe this error is also related to #1418 where FixedValueParameter<T> was introduced.

Change in r5848 is difficult to understand.

[mkommend]

r6019: Corrected bug in TypeSelector.

[mkommend]

Thx for the testing Andreas. The revision r5848 is quite simple to explain; it only removes unnecessary checks (line 122 -124), makes the try-catch block (line 134 - 140) obsolete by checking for a default constructor and configures the nested type selector correctly.

[abeham]

I tested it again: Creating a ValueParameter<SingleSuccessorOperator> results in an exception. Here is the exception message:

TargetInvocationException: Exception has been thrown by the target of an invocation.
   at System.RuntimeMethodHandle._InvokeConstructor(IRuntimeMethodInfo method, Object[] args, SignatureStruct& signature, RuntimeType declaringType)
   at System.RuntimeMethodHandle.InvokeConstructor(IRuntimeMethodInfo method, Object[] args, SignatureStruct signature, RuntimeType declaringType)
   at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
   at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
   at System.Activator.CreateInstance(Type type, Object[] args)
   at HeuristicLab.Core.Views.CreateParameterDialog.get_Parameter()
-----
MemberAccessException: Cannot create an instance of HeuristicLab.Operators.SingleSuccessorOperator because it is an abstract class.
   at System.Reflection.RuntimeConstructorInfo.CheckCanCreateInstance(Type declaringType, Boolean isVarArg)
   at System.Reflection.RuntimeConstructorInfo.ThrowNoInvokeException()
   at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Reflection.ConstructorInfo.Invoke(Object[] parameters)
   at HeuristicLab.Parameters.ValueParameter`1.CreateDefaultValue()
   at HeuristicLab.Parameters.ValueParameter`1..ctor(String name, String description)

I think a check for abstract types is missing before invoking the constructor.

[mkommend]

r6025: Added a check for abstract types in ValueParameter.CreateDefaultValue.

[abeham]

Very well I think that should do it. Great feature, thx for implementing it!