C# LANGUAGE SPECIFICATION
For a method invocation, the primary-expression of the invocation-expression must be a method group. The method group identifies the one method to invoke or the set of overloaded methods from which to choose a specific method to invoke. In the latter case, determination of the specific method to invoke is based on the context provided by the types of the arguments in the argument-list.
The compile-time processing of a method invocation of the form M(A), where M is a method group and A is an optional argument-list, consists of the following steps:
The set of candidate methods for the method invocation is constructed. Starting with the set of methods associated with M, which were found by a previous member lookup (§7.3), the set is reduced to those methods that are applicable with respect to the argument list A. The set reduction consists of applying the following rules to each method T.N in the set, where T is the type in which the method N is declared:
If N is not applicable with respect to A (§220.127.116.11), then N is removed from the set.
If N is applicable with respect to A (§18.104.22.168), then all methods declared in a base type of T are removed from the set.
If the resulting set of candidate methods is empty, then no applicable methods exist, and a compile-time error occurs. If the candidate methods are not all declared in the same type, the method invocation is ambiguous, and a compile-time error occurs (this latter situation can only occur for an invocation of a method in an interface that has multiple direct base interfaces, as described in §13.2.5).
The best method of the set of candidate methods is identified using the overload resolution rules of §7.4.2. If a single best method cannot be identified, the method invocation is ambiguous, and a compile-time error occurs.
Given a best method, the invocation of the method is validated in the context of the method group: If the best method is a static method, the method group must have resulted from a simple-name or a member-access through a type. If the best method is an instance method, the method group must have resulted from a simple-name, a member-access through a variable or value, or a base-access. If neither of these requirements are true, a compile-time error occurs.
Once a method has been selected and validated at compile-time by the above steps, the actual run-time invocation is processed according to the rules of function member invocation described in §7.4.3.
The intuitive effect of the resolution rules described above is as follows: To locate the particular method invoked by a method invocation, start with the type indicated by the method invocation and proceed up the inheritance chain until at least one applicable, accessible, non-override method declaration is found. Then perform overload resolution on the set of applicable, accessible, non-override methods declared in that type and invoke the method thus selected.
22.214.171.124 Delegate invocations
For a delegate invocation, the primary-expression of the invocation-expression must be a value of a delegate-type. Furthermore, considering the delegate-type to be a function member with the same parameter list as the delegate-type, the delegate-type must be applicable (§126.96.36.199) with respect to the argument-list of the invocation-expression.
The run-time processing of a delegate invocation of the form D(A), where D is a primary-expression of a delegate-type and A is an optional argument-list, consists of the following steps:
D is evaluated. If this evaluation causes an exception, no further steps are executed.
The value of D is checked to be valid. If the value of D is null, a System.NullReferenceException is thrown and no further steps are executed.
Otherwise, D is a reference to a delegate instance. Function member invocations (§7.4.3) are performed on each of the callable entities in the invocation list of the delegate. For callable entities consisting of an instance and instance method, the instance for the invocation is the instance contained in the callable entity.
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