Re^5: A short, "iffy" rant

in reply to Re^4: A short, "iffy" rant
in thread A short, "iffy" rant

What problem were you trying to address when you wrote this?

Modularity, Maintenance - the usual suspects. Exporter::Dispatch isn't really aimed at dispatch tables of 3 or 4 subs of 1 line a piece - its aimed for use with large dispatch tables. For instance, the last time I used it was on a project with 4 dispatch tables, each having between 10-30 subroutines, with each subroutine varying in length from 10-60 lines.

As for closing over lexical variables, you can still do that if the subs are in a separate package - you just put the declaration in the same package as the rest of the dispatch table subs are defined!

But, as for:

And a further hash advantage - you are allowed names that would not easy or (in some cases) legal in Perl function names.

What does that buy you? The only time I think I've ever used a dispatch table that had non-word dispatch names was this:

my %op_table = (
    '+' =>  sub { $_[0] +  $_[1] },
    '-' =>  sub { $_[0] -  $_[1] },
    '*' =>  sub { $_[0] *  $_[1] },
    '>' =>  sub { $_[0] >  $_[1] },
    '<' =>  sub { $_[0] <  $_[1] },
    '=' =>  sub { $_[0] == $_[1] }, # this is the one oddball;
                                    # otherwise i could just eval'ed..
+.
    '<=' => sub { $_[0] <= $_[1] },
    '>=' => sub { $_[0] >= $_[1] },
    '!=' => sub { $_[0] != $_[1] },
);
[download]

This was part of a very simple simulator that I wrote for a language that we have compiled down to 68HC11, and the only reason I wrote it this way was so I could use the raw token as the hash key.

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Re^6: A short, "iffy" rant by tilly (Archbishop) on Oct 18, 2004 at 16:14 UTC
Non-word dispatch names make sense if you want to dispatch on the name of a condition, and the most convenient names that make sense are driven by external data. For instance they may be driven off of filenames, which include characters like . and - in the names. For another instance, take a look at Why I like functional programming. Most of the names there are pieces of HTML tags. It is a piece of flexibility that you may not need most of the time, but when you do it is a lifesaver. As for length, if your dispatch table is so long that you want to put it into another file, nothing stops you from doing so. I think that the ease of doing it is pretty much equivalent with either syntax. If you really want the `sub foo {...}` syntax, then you can do it by adding a function called "new", and using OO to dynamically do the dispatch.	[reply] [d/l]

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Re^6: A short, "iffy" rant
by tilly (Archbishop) on Oct 18, 2004 at 16:14 UTC

For instance they may be driven off of filenames, which include characters like . and - in the names. For another instance, take a look at Why I like functional programming. Most of the names there are pieces of HTML tags.

It is a piece of flexibility that you may not need most of the time, but when you do it is a lifesaver.

As for length, if your dispatch table is so long that you want to put it into another file, nothing stops you from doing so. I think that the ease of doing it is pretty much equivalent with either syntax. If you really want the sub foo {...} syntax, then you can do it by adding a function called "new", and using OO to dynamically do the dispatch.

[reply]
[d/l]

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