Note: information on this page refers to Ceylon 1.0, not to the current release.


Invocation is the act of calling something that is Callable.


Invocation using a positional argument list, in parentheses:

put(1, "one")

Invocation using a named argument list, in braces:

put {


The thing that is being invoked is called the primary of the invocation. It is followed by an argument list.

The type of an invocation expression is the return type of the callable type of the primary. For example, the return type of a function being invoked, or the type of a class being instantiated.

Function and method invocation

Function and method invocation is direct invocation, and therefore supports named argument lists.

Class invocation

Invoking a class (instantiating it) creates a new instance of the class.

Class invocation is a direct invocation, and therefore supports named argument lists.

Indirect invocation

You can invoke a value that has a Callable type:

Callable<Anything, []> fn = // ...
Anything result = fn();

Because the Callable type does not retain any information about the parameter names, and cannot use a named argument invocation; only positional arguments.

The Callable type can encode information about defaulted parameters, so the invocation need not specify arguments for parameters which are defaulted:

Callable<Anything, [String=]> defaulted = // ...
variable Anything result = defaulted();
result = defaulted("an argument");

Multiple argument lists

Because a Callable can itself have a Callable return type you sometimes see invocations with multiple parameter lists:

String(String)(Integer) higher = // ...
String result = higher(1)("");

Note that the type abbreviation for Callable means that the argument lists appear in reversed order because String(String)(Integer) is parsed as Callable<Callable<String, [String]>, [Integer]>

Named argument lists are only allowed as the first argument list in an invocation using multiple argument lists, because the second invocation is an indirect invocation.

Tuple and Iterable enumeration

Technically, tuple and iterable enumerations are also invocations.

See also