Does constructor with optional-parameter overload it?

Question

Here is an example of code:

public List(int capacity = defaultCapacity) {
    items = new T[capacity];
}

In C# 5 Language Specification Section 1.6.7 is written:

Instance constructors can be overloaded. For example, the List class declares two instance constructors, one with no parameters and one that takes an int parameter.

But compiled IL for this code doesn't contain 2 constructors. It contains only this declaration:

.method public hidebysig specialname rtspecialname 
        instance void  .ctor([opt] int32 capacity) cil managed

It means that optional parameter is CLR level and is defined by [opt].

After CLR there is no runtime that can represent this object with 2 overloaded constructors.

For Example if I am creating 2 separate constructors without optional parameter compiled IL will contain 2 .ctor -s.

I want to clarify, if language specification is saying that class declares two instance constructors doesn't it mean that compiled IL will contain 2 ctor-s too.

The "real" `List` in mscorlib.dll does have those 2 constructors, but the _example_ `List` in the spec section only has a single constructor, so it's confusing. To add to that, the spec labels that single constructor as "Constructors" (plural). Go figure. — Eren Ersönmez, Aug 25 '15 at 17:38
@MarcinJuraszek You're right. I meant "those" 2 constructors in the example they mention. — Eren Ersönmez, Aug 25 '15 at 17:41
Is there any method to report this small issue in specification ? — bot_insane, Aug 25 '15 at 17:42

MarcinJuraszek · Accepted Answer · 2015-08-25T17:31:39.100

Optional parameters, no matter if used on methods or constructors, do not introduce additional overloads. Instead, optional parameters are marked with [opt], and whenever you call it without that parameter value specified that optional value will be included in your compiled code.

Because of that when you change default value of optional parameters you need to recompile all the usages, to get that new value injected into all the calls. If you don't do that old value will be used.

Update

Quote from the spec is confusing. If it talks about List<T> defined in 1.6.7 with just one constructor, with optional parameter, than it's wrong.

Does constructor with optional-parameter overload it?

1 Answers1