Chapter91:OverloadResolution

Section91.1:BasicOverloadingExample
ThiscodecontainsanoverloadedmethodnamedHello:

classExample

{

publicstaticvoidHello(intarg)

{

Console.WriteLine(“int”);

}

publicstaticvoidHello(doublearg)

{

Console.WriteLine(“double”);

}

publicstaticvoidMain(string[]args)

{

Hello(0);

Hello(0.0);

}

}

WhentheMainmethodiscalled,itwillprint

int

double

Atcompile-time,whenthecompilerfindsthemethodcallHello(0),itfindsallmethodswiththenameHello.In thiscase,itfindstwoofthem.Itthentriestodeterminewhichofthemethodsisbetter.Thealgorithmfor determiningwhichmethodisbetteriscomplex,butitusuallyboilsdownto”makeasfewimplicitconversionsas possible”.
Thus,inthecaseofHello(0),noconversionisneededforthemethodHello(int)butanimplicitnumeric conversion is needed for the method Hello(double). Thus, the first method is chosen by the compiler.

InthecaseofHello(0.0),thereisnowaytoconvert0.0toanintimplicitly,sothemethodHello(int)isnoteven consideredforoverloadresolution.Onlymethodremainsandsoitischosenbythecompiler.
Section91.2:”params”isnotexpanded,unlessnecessary
Thefollowing program:

classProgram

{

staticvoidMethod(paramsObject[]objects)

{

System.Console.WriteLine(objects.Length);

}

staticvoidMethod(Objecta,Objectb)

{

System.Console.WriteLine(“two”);

}

staticvoidMain(string[]args)

{

object[]objectArray=newobject[5];

Method(objectArray);

Method(objectArray,objectArray);

Method(objectArray,objectArray,objectArray);

}

}

willprint:

5

two

3

ThecallexpressionMethod(objectArray)couldbeinterpretedintwoways:asingleObjectargumentthathappens to be an array (so the program would output 1because that would be the number of arguments, or as an array of arguments, given in the normal form, as though the method Methoddid not have the keyword params. In these situations, the normal, non-expanded form always takes precedence. So, the program outputs 5.

In the second expression, Method(objectArray,objectArray), both the expanded form of the first method and thetraditionalsecondmethodareapplicable.Inthiscasealso,non-expandedformstakeprecedence,sothe program prints two.
Inthethirdexpression,Method(objectArray,objectArray,objectArray),theonlyoptionistousetheexpanded formofthefirstmethod,andsotheprogramprints3.
Section91.3:Passingnullasoneofthearguments
If you have

voidF1(MyType1x){

//dosomething

}

voidF1(MyType2x){

//dosomethingelse

}

andforsomereasonyouneedtocallthefirstoverloadofF1butwithx=null,thendoingsimply

F1(null);

willnotcompileasthecallisambiguous.Tocounterthisyoucan do

F1(nullasMyType1);