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Edit section on generic functions

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* doc/ref/goops.texi (Generic Functions and Accessors): Renamed from
  `Creating Generic Functions'.  Explain what an accessor is.
  (Basic Generic Function Creation): Clarify the point of the text
  about generics having short names.
This commit is contained in:
Neil Jerram 2010-10-03 23:22:03 +01:00
parent 647db87dbc
commit 17285a7c49
1 changed files with 28 additions and 12 deletions
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40
doc/ref/goops.texi
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@ -35,7 +35,7 @@ overriding or redefining those methods.
* Defining New Classes::
* Creating Instances::
* Accessing Slots::
* Creating Generic Functions::
* Generic Functions and Accessors::
* Adding Methods to Generic Functions::
* Invoking Generic Functions::
* Redefining a Class::
@ -748,15 +748,25 @@ The default methods all call @code{goops-error} with an appropriate
message.
@end deffn
@node Creating Generic Functions
@section Creating Generic Functions
@node Generic Functions and Accessors
@section Generic Functions and Accessors
A generic function is a collection of methods, with rules for
determining which of the methods should be applied for any given
invocation of the generic function.
invocation of the generic function. GOOPS represents generic functions
as metaobjects of the class @code{<generic>} (or one of its subclasses).
GOOPS represents generic functions as metaobjects of the class
@code{<generic>} (or one of its subclasses).
An accessor is a generic function that can also be used with the
generalized @code{set!} syntax (@pxref{Procedures with Setters}). Guile
will handle a call like
@example
(set! (@code{accessor} @code{args}@dots{}) @code{value})
@end example
@noindent
by calling the most specialized method of @code{accessor} that matches
the classes of @code{args} and @code{value}.
@menu
* Basic Generic Function Creation::
@ -813,13 +823,19 @@ including an existing generic function or accessor, is overwritten by
the new definition.
@end deffn
It is sometimes tempting to use GOOPS accessors with short names. For
example, it is tempting to use the name @code{x} for the x-coordinate
in vector packages.
GOOPS generic functions and accessors often have short, generic names.
For example, if a vector package provides an accessor for the X
coordinate of a vector, that accessor may just be called @code{x}. It
doesn't need to be called, for example, @code{vector:x}, because
GOOPS will work out, when it sees code like @code{(x @var{obj})}, that
the vector-specific method of @code{x} should be called if @var{obj} is
a vector.
Assume that we work with a graphical package which needs to use two
independent vector packages for 2D and 3D vectors respectively. If
both packages export @code{x} we will encounter a name collision.
That raises the question, however, of what happens when different
packages define a generic function with the same name. Suppose we
work with a graphical package which needs to use two independent vector
packages for 2D and 3D vectors respectively. If both packages export
@code{x} we will encounter a name collision.
This can be resolved automagically with the duplicates handler
@code{merge-generics} which gives the module system license to merge