com.blackperl.Perl
Interface MapBlock

public interface MapBlock

Interface expected by methods in the Map class. When using the map function (see Map), the data returned by the evaluation function may actually be more items than are processed as inputs. This is a common idiom in Perl, often used in the creation of associate arrays (the Perl equivalent of java.util.HashTable). Because of this, map and grep (see Grep) use different interfaces for the specification of the evaluation objects they operate upon.

To allow a map operation to potentially generate more items than it is fed, the signature of the eval method dictates that the return value is an array. Though this may be inconvenient for code that implements 1-to-1 mapping, it allows maximum flexibility. In cases where the programmer knows for certain that the map usage will only need to do a 1-to-1 data mapping, map can also accept a GrepBlock instance.

The MapBlock interface faces the same block-based limitations as GrepBlock. In particular, while this can be used in the declaration of anonymous inner-classes on the fly, these classes are limited in what values from the current lexical scope can be accessed. Only those values that are declared both final and static may be referenced in one of these inner-classes. The solution to this is to use the interface in the declaration of a named inner-class, one that defines its own members and methods. This can then be used to encapsulate the local information that needs to be passed to the particular call to map. For an example of this, see GrepBlock.

Method Summary

java.lang.Object[]

eval(java.lang.Object object) When the map function is called with an object implementing this interface, this is the function it will expect to be able to invoke for each element in the list it also receives.

Method Detail

eval

public java.lang.Object[] eval(java.lang.Object object)

When the map function is called with an object implementing this interface, this is the function it will expect to be able to invoke for each element in the list it also receives. The implementing class should provide this such that it takes a single argument, and returns an array of zero or more objects (or null, which is also acceptable).

Parameters:

object - An arbitrary object passed in by map

Returns:

An array of arbitrary objects, based on the functionality this method implements