c# - BindingFlags.OptionalParameterBinding varying behaviour in different frameworks. Bug in .NET? -

i've tried force activator.createinstance use constructor default parameters.

i've found suggestion, repeated few times on (first comment) http://connect.microsoft.com/visualstudio/feedback/details/521722/system-activator-createinstance-throws-system-missingmethodexception-with-constructor-containing-an-optional-parameter

i wanted run on mono , didn't work, throwing missingmethodexception. before filing bug i've made experiment on .net 4.5:

class program {     static void main(string[] args)     {         new a();         activator.createinstance(typeof(a),             bindingflags.createinstance              | bindingflags.public              | bindingflags.instance             | bindingflags.optionalparambinding,             null, new object[] {type.missing}, null);     } } class {     public a()     {         console.writeline("first");     }     public a(int = 5)     {         console.writeline("second");     } } 

of course, result predictable:

first second 

then i've tried remove type.missing parameter see happens, hoping find way invoke constructor varying number of default parameters.

i flabbergasted see nothing changed! passing new object[]{} i've expected:

first first 

wondering type.missing do, and, golly!, why mentioned in examples on internet, i've changed framework.

on .net 4.0 same, on .net 3.5 result was

first first 

this seems odd. there documented reasons of such behaviour?

what proper way call constructor possibly many optional parameters?