Param Array and Ellipsis
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The latest version of this topic can be found at Param Array and Ellipsis.
Precedence of the param array for resolving overloaded function calls has changed from Managed Extensions for C++ to Visual C++.
In both Managed Extensions and the new syntax, there is no explicit support for the param array that C# and Visual Basic support. Instead, one flags an ordinary array with an attribute, as follows:
void Trace1( String* format, [ParamArray]Object* args[] );
void Trace2( String* format, Object* args[] );
While these both look the same, the ParamArray attribute tags this for C# or other CLR languages as an array taking a variable number of elements with each invocation. The change in behavior in programs between Managed Extensions and the new syntax is in the resolution of an overloaded function set in which one instance declares an ellipsis and a second declares a ParamArray attribute, as in the following example provided by Artur Laksberg.
int fx(...); // 1
int fx( [ParamArray] Int32[] ); // 2
In Managed Extensions, the ellipsis was given precedence over the attribute which is reasonable since the attribute is not a formal aspect of the language. However, in the new syntax, the param array is now supported directly within the language, and it is given precedence over the ellipsis because it is more strongly typed. Thus, in Managed Extensions, the call
fx( 1, 2 );
resolves to fx(…) while in the new syntax, it resolves to the ParamArray instance. On the off chance that your program behavior depends on the invocation of the ellipsis instance over that of the ParamArray, you will need to modify either the signature or the call.