7.4.2 Overload resolution
Overload resolution is a compile-time mechanism for selecting the best function member to invoke given an argument list and a set of candidate function members. Overload resolution selects the function member to invoke in the following distinct contexts within C#:
- Invocation of a method named in an invocation-expression (Section 7.5.5).
- Invocation of an instance constructor named in an object-creation-expression (Section 184.108.40.206).
- Invocation of an indexer accessor through an element-access (Section 7.5.6).
- Invocation of a predefined or user-defined operator referenced in an expression (Section 7.2.3 and Section 7.2.4).
Each of these contexts defines the set of candidate function members and the list of arguments in its own unique way, as described in detail in the sections listed above. For example, the set of candidates for a method invocation does not include methods marked
override (Section 7.3), and methods in a base class are not candidates if any method in a derived class is applicable (Section 220.127.116.11).
Once the candidate function members and the argument list have been identified, the selection of the best function member is the same in all cases:
- Given the set of applicable candidate function members, the best function member in that set is located.
- If the set contains only one function member, then that function member is the best function member.
- Otherwise, the best function member is the one function member that is better than all other function members with respect to the given argument list, provided that each function member is compared to all other function members using the rules in Section 18.104.22.168.
- If there is not exactly one function member that is better than all other function members, then the function member invocation is ambiguous and a compile-time error occurs.
The following sections define the exact meanings of the terms applicable function member and better function member.