1. RE: Type Class!
- Posted by tacitus <indorlaw at zdnetonebox.com>
Mar 17, 2001
-
Last edited Mar 18, 2001
i was interested in types as well - but soon came to the conclusion that
they are really just functions disguised in a slightly different syntax.
the refman hints at this. mts's post simply confirms my view.
to demonstrate, i was writing a library routine for dos that parsed an
html file into a file readable by dos. i defined a number of tags as
the type line_break, something like this:-
type line_break(sequence tag)
if equal(tag, "<br>")
or equal(tag, "<p>")
or equal(tag, "<div>") then
return 1
else return 0
end if
end type
(i could have done better by replacing the if statement with:-
return equal(tag, "<br>") or equal(tag, "<p>") or equal(tag, "<div>")
)
i could test whether a tag was a line break with:-
if line_break(tag) then etc
i suddenly realised that the same thing could always be done better with
a function.
function line_break(sequence tag)
-- if statement as above
return 1
else return 0
end function
then test for line break with:
if line_break(tag) then etc
note the similarity. my example is more like the traditional view of a
type, but mts's examples demonstrate better the relationship with a
function.
the only difference i can see between a type and a function is that
types provide error checking by the interpreter, while with functions
you define your own error checking (or have none at all). generally, i
would have thought that your own error checking will be more graceful,
as the program can run to its conclusion or otherwise on your say-so.
i agree there's nothing to be afraid of with types, but also not much to
be excited about.
cheers
tacitus
Mike The Spike wrote:
> Here's a little trick I fished up just now...
>
> You like VB huh?
> You like it when you can create a property, and set
> and get the status of a variable...
> Confused?
> No problem, Eu can do that too!
>
> Here it is...
> If you didn't know you could do this (people are
> afraid of using 'type' nowadays), you'll think how you
> could miss this cool feature of Eu's.
>
> Ok...
> What if you'd want a variable, that when assigned a
> value, it autmatically processes that data using your
> own specifc code?
> An example?
> Here ya go.
>
> type type_writer(sequence s)
> puts(1,s)
> return 1
> end type
>
>
> Now simply say;
>
> type_writer echo
> echo = "Hello World!"
>
>
> What happens?
> "Hello World!" is printed to the screen.
> Also usefull for doing Memory Dumping.
> Keep track of each value assigned to a variable, by
> writing them to disk.
>
> Wouldn't it be cool to do 'classes' in Eu, FOR REAL?
> Well, you can!
> Like this;
>
> type class(sequence func)
> call_proc(func,func[2])
> return 1
> end type
>
> Now you can do this!;
>
> class myclass
> myclass = {"MyPuts","Hello World!"}
>
> After this assignement,
> routine 'MyPuts' is called with "Hello World!", thus
> writing this string to the screen (assuming that's
> what MyPuts does).
>
>
> That ain't all folks...
> There *LOADS* of things you can do with types...
> Go ahead!
> Try it!
> Classes, properties, debugging, resource tracking,
> ByRef passing (routine_id works on types aswell!!),
> etc...
> There's no limits, just your own imagination.
>
> So go ahead!
> Types won't bite!
>
>
> Mike The Spike
> PS. Don't forget to use 'without type_check' for extra
> speed boosts!
>
>
>
