This reference page describes how arrange for OTcl classes and their methods to be demand loaded. The mechanism extends the existing Tcl autoloading scheme (with which you should be familiar) by using an otcl_mkindex procedure to add entries to a tclIndex file. It allows you to distribute classes across files without additional concern for inheritance dependencies, as well as distribute a class's methods across files.
To add OTcl load entries to a tclIndex, use the otcl_mkindex procedure, defined during OTcl initialization. For example, to update the tclIndex in the current directory for the demand loading of classes, issue this shell command:
echo "otcl_mkindex Class . *.tcl" | otclsh
otcl_mkindex takes the same directory and filename pattern arguments as auto_mkindex, but also takes a list of classes as its first argument. This list, the creator list, describes the kind of objects that are candidates for demand loading. Usually this will be Class, as above, to cause index entries to be generated for classes. But it may also specify other classes if you are working with meta-classes or need loading for regular objects. otcl_mkindex appends the tclIndex file directly, and returns a string describing the number of object and method index entries it generated.
Like auto_mkindex, otcl_mkindex will only find obvious candidates for demand loading. Both explicit creation, via the create method, and implicit creation, via a method name that is not a known method of Class, are considered in the search. Objects (but not methods) must be created at the hard left margin, and object and method names may not begin with "$".
Autoloading of class and object commands is triggered via the regular Tcl unknown mechanism, so that invoking a missing class or object command will cause it to be loaded. In addition, OTcl demand loads in two other ways.
First, unknown classes referenced as superclasses will be demand loaded. This is triggered internally by the OTcl system. It means that you can distribute classes across files without concern for sourcing the files in inheritance order. It does not mean, however, that you can make forward references to classes within a file, or mutually recursive forward references across files.
Second, undefined methods may be demand loaded when they are invoked. This is arranged for autoloaded classes by the OTcl object loader, otcl_load. It means that you can distribute the definition of a class and its methods over more than one file.
Method level loading works as follows. When a class or object is being autoloaded by otcl_load, only those methods defined in the main class file that is sourced will be fully loaded. Other methods that are known to exist because of auto_index entries are then filled with load stubs by using the auto option of the proc and instproc methods. This guarantees that if they are invoked, they will be loaded. Note that these method load stubs must be installed, rather than relying on an unknown-style load scheme, to cater for the shadowing of methods. Also, you can control your own load policy by rewriting otcl_load.