ref: 75c92428225428c8fde2d015f010e608a0b12f1d
dir: purgatorio/man/2/sys-self
.TH SYS-SELF 2
.SH NAME
SELF \- reference self as a compatible module type
.SH SYNOPSIS
.B
include "sys.m";
.br
.BI "me := load" " Module " SELF;
.SH DESCRIPTION
An instance of
a module of one type can acquire a reference to itself as any compatible module type,
using the Limbo
.B load
operator with the special built-in module name
.BR $self .
Normally, applications use a synonym, the constant
.BR SELF ,
which is defined by
.B sys.m
.I outside
the declaration of the
.B Sys
module
(so that it need not be imported).
Note that the result of the
.B load
refers to the same instance
that is currently executing (ie, the same module data).
.PP
This mechanism is most often used to obtain a reference to the current module
instance with a
.I 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:
.IP
.EX
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);
};
.EE
.PP
an instance of module
.B T
can execute both the following:
.IP
.EX
t := load T SELF;
s := load S SELF;
.EE
.PP
but a module of type
.B S
could not load itself as type
.BR T .
.PP
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:
.IP
.EX
g := load G "g.dis";
g->init(s);
.EE
.PP
See the definition and use of
.B BufioFill
in
.IR bufio (2)
and
.IR bufio-chanfill (2)
for a practical example.
.SH SEE ALSO
``The Limbo Programming Language'', Volume 2.