NAME

SELF - reference self as a compatible module type

SYNOPSIS

include "sys.m";
me := load Module SELF;

DESCRIPTION

An instance of a module of one type can acquire a reference to itself as any compatible module type, using the Limbo load operator with the special built-in module name $self. Normally, applications use a synonym, the constant SELF, which is defined by sys.m outside the declaration of the Sys module (so that it need not be imported). Note that the result of the load refers to the same instance that is currently executing (ie, the same module data).

This mechanism is most often used to obtain a reference to the current module instance with a restriction of its module type to a compatible subtype (eg, containing a subset of the current module's declarations). For example, given modules of the following types:

T: module
{
    init:    fn(nil: ref Draw->Context, nil: list of string);
    special: fn(a, b: int);
};
S: module
{
    special: fn(x, y: int);
};
G: module
{
    init:    fn(v: S);
};

an instance of module T can execute both the following:

t := load T SELF;
s := load S SELF;

but a module of type S could not load itself as type T.

The result might typically be assigned to a module variable of that type (including passing as a parameter or storing in an adt), as in:

g := load G "g.dis";
g->init(s);

See the definition and use of BufioFill in bufio(2) and bufio-chanfill(2) for a practical example.

SEE ALSO

``The Limbo Programming Language'', Volume 2.

SYS-SELF(2 )

Rev:  Tue Mar 31 02:42:39 GMT 2015