Order now 3rd edition Overloading Just as a reminder, overloading is what happens when you have two methods with the same name but different signatures. At compile timethe compiler works out which one it's going to call, based on the compile time types of the arguments and the target of the method call.

I'm assuming you're not using dynamic here, which complicates things somewhat. Now, things can get a little bit confusing sometimes when it comes to resolving overloads This article will point out some of the gotchas you might run into For that, read the specification - but be aware that you may get lost in a fairly complex topic.

Overloading interacts with things like type inference and implicit conversions including lambda expressions, anonymous methods and method groups, all of which can become tricky.

All specification references are from the C 4 spec. This article is also not going to go into the design choices of when it's appropriate and when it's not. I'll give a little advice about when it might be potentially very confusing to use overloading, but anything beyond that will have to wait for another time.

I will say that in general I believe overloading should be used for convenience, usually with all overloads ending up calling one "master" method. That's not always the case, but I believe it's the most common scenario which is appropriate. In each example, I'll give a short program which will declare some methods and call one - and then I'll explain what gets called in which version of Cand why.

As I'm not trying to focus on the design decisions but merely the mechanical choices the C compiler makes, I haven't tried to make the examples do anything realistic, or even given them realistic names: Of course the action taken is irrelevant, but it makes it easier to grab the code and experiment with it if you want to. Let's start off with a couple of really simple cases, just to get into the swing of things.

First, the trivial case where only one overload is possible at all.

This will print Foo string y - there's no implicit string conversion from string the type of the argument here, "text" to intso the first method isn't an applicable function member in spec terminology section 7. Overloading ignores any methods which can't be right when it's deciding which one to call. This time, Foo int x will be printed.

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The compiler decides which one to pick based on the better function member rules section 7. There are more rules section 7. When there are multiple parameters involved, for one method to "beat" another one it has to be at least as good for each parameter, and better for at least one parameter. This is done on a method-by-method comparison: Here the first method Foo int x, int y wins because it beats the second method on the second parameter, and the third method on the first parameter.

Inheritance can cause a confusing effect. When the compiler goes looking for instance method overloads, it considers the compile-time class of the "target" of the call, and looks at methods declared there.

If it can't find anything suitable, it then looks at the parent class This means that if there are two methods at different levels of the hierarchy, the "deeper" one will be chosen first, even if it isn't a "better function member" for the call. Here's a fairly simple example:. The target of the method call is an expression of type Childso the compiler first looks at the Child class.

There's only one method there, and it's applicable there's an implicit conversion from int to double so that's the one that gets picked. The compiler doesn't consider the Parent method at all.

The reason for this is to reduce the risk of the brittle base class problem, where the introduction of a new method to a base class could cause problems for consumers of classes derived from it. Eric Lippert has various posts about the brittle base class problem which I can highly recommend. There's one aspect of this behaviour which is particularly surprising though. What counts as a method being "declared" in a class?

It turns out that if you override a base class method in a child class, that doesn't count as declaring it. Let's tweak our example very slightly:.

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Now it looks like you're trying to call Child. Two tails market/eatery woodstock il int x in my opinion - but the above code will actually print Child.

Functions

The compiler ignores the overriding method in the child. Given this oddness, my advice would be to avoid overloading across inheritance boundaries You'll be glad to hear that the rest of the examples stock market basics stories this page don't use inheritance. The return type of a method is not considered to be part of a method's signature section 3.

In other words, it's not part of the test for an applicable function member. Here the overload of string Foo int x is chosen and then the compiler works out that it can't assign a string to a variable of type Guid.

On its own, the Guid Foo double y would be fine, but because the other method was better in terms of argument conversions, it doesn't have a chance. Optional parameters, introduced into C 4, allow a method to declare a default value for some or all of its parameters. The caller can then omit the corresponding arguments if they're happy with the defaults. This affects overload resolution as standard chartered ftse share price may be multiple methods with a different number of parameters which are all applicable.

When faced with a choice between a method which requires the compiler to fill in optional parameter values and one which doesn't, if the methods are otherwise "tied" i.

Out parameters should imply Optional

When considering the first method, the compiler would need to fill in the argument for the y parameter using the default value - whereas the second method doesn't require this. The output is therefore Foo int x. This call is ambiguous, because the one optional output parameter c# which has been given discount brokers futures fine for both methods, and both eur/usd forecast fx empire extra arguments which would be filled in from default values.

The fact that the first method would need two arguments to be defaulted and the second would only need one is irrelevant. Just to be clear, this tie breaking only comes in after the methods have been compared to each other using the pre-C 4 rules. So, let's change our earlier example a little:.

This time the method with the optional parameter is used because the int to int conversion is preferred over the int to double one. Named arguments - another feature introduced in C 4 - can be used to effectively reduce the set of applicable function members by ruling out ones which have the "wrong" parameter names.

Here's a change to an early simple example - all I've done is change the calling code to specify an argument name.

This time the first method isn't applicable, because there's no y parameter Obviously this technique only works if the parameters in the methods have different names though. Sometimes, the language changes so that a new conversion is available. This is a breaking change, as it means that overloads which were previously not applicable function members can become applicable.

It doesn't even have to be a better conversion than any existing overloads - if you have a child class with a method which was previously inapplicable, and it becomes applicable, then that will take precedence over any methods in the base class, as we've already seen.

In C 2 this occurred with delegates - you could suddenly build a MouseEventHandler instance from a method with a signature of void Foo object sender, EventArgs ewhereas in C 1 this wasn't allowed. In C 4 there's a more widely-applicable kind of conversion which is now available: The C 3 compiler will pick the overload Foo object x. The C 4 compiler, when targeting. This change occurs with no warnings of any kind. This article may well expand over time, covering other oddities such as params parameters, for example but I hope I've given enough to think about for the moment.

Basically, overloading is a minefield with lots of rules which can interact in evil ways. While overloading can certainly be useful, I've found that often it's better to create alternative methods with clear names instead. This is particularly useful for constructors, and can be a helpful technique when you would otherwise want to declare two constructors with identical signatures: The debate about static factory methods vs publicly accessible constructors is one for a different article, however.

Overloading causes a lot less of a problem when only one method will ever be applicable - for example when the parameter types are mutually incompatible one method taking an int and one taking a string for example or there are more parameters in one method than another. Even so, use with care: If you find yourself going to the spec to see which of your methods will be called and the methods are under your control then I would strongly advise you to consider renaming some of the methods to reduce the degree of overloading.

This advice goes double when it's across an inheritance hierarchy, for reasons outlined earlier. About Book Contents Reviews Notes Errata Articles Talks Downloads Resources Code Formatter Order now 3rd edition. Overloading Just as a reminder, overloading is what happens when you have two methods with the same name but different signatures.

Simple cases Let's start off with a couple of really simple cases, just to get into the swing of things.