http://qs1969.pair.com?node_id=417951


in reply to Mutator chaining considered harmful

Chained mutators can Here's a snippet from my own code. This probes a real-time audio application with a five channel OpenGL oscilloscope: 
  my $s= Scope->new('probe' => $netlist)
            ->anatrace('in', 'System input', 'active', 1)
            ->anatrace('out_1', 'Lpf bank1', 'active', 1)
            ->anatrace('out_2', 'Lpf bank2', 'active', 1024)
            ->anatrace('out', 'System output', 'active', 1)
            ->anatrace('bank2', 'Switch pos', 'active', 1)
            ->generate();

[download]
Want to see another channel? Call anatrace again.

I don't think that features with potential downsides should be 'considered harmful'.

It is possible to create a 'little language' out of chained method calls. I avoid creating little languages because I have seen a few of them grow into voracious blood-sucking monsters. I can enjoy chaining method calls without fear of triggering a science-related memetic disorder.

It should work perfectly the first time! - toma

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Re^2: Mutator chaining considered harmful
by kappa (Chaplain) on Dec 29, 2004 at 14:11 UTC
    This gives you almost nothing in comparison with: 
    ...
$s->anatrace('bank2', 'Switch pos', 'active', 1);
$s->generate();

    [download]
    And when the objects have long names or are expressions you can always: 
    for (Scope->new('probe' => $netlist)) {
    $_->anatrace('in', 'System input', 'active', 1);
    ...
    $_->generate();
}

    [download]
    --kap
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[d/l]
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Re^2: Mutator chaining considered harmful
by Aristotle (Chancellor) on Dec 29, 2004 at 19:39 UTC

    Apart from kappa's points: read my root node update. Here's what that would look like with a good interface:

    my $s = Scope->new( 'probe' => $netlist );
$s->anatrace(
    in    => [ 'System input', 'active', 1 ],
    out_1 => [ 'Lpf bank1', 'active', 1 ],
    out_2 => [ 'Lpf bank2', 'active', 1024 ],
    out   => [ 'System output', 'active', 1 ],
    bank2 => [ 'Switch pos', 'active', 1 ],
);
$s->generate();

    [download]

    Makeshifts last the longest.

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[d/l]
      I suppose I could also use this :-) 
      my $s = Scope->new( probe => $netlist )
             ->anatrace(
                 in    => [ 'System input', 'active', 1 ],
                 out_1 => [ 'Lpf bank1', 'active', 1 ],
                 out_2 => [ 'Lpf bank2', 'active', 1024 ],
                 out   => [ 'System output', 'active', 1 ],
                 bank2 => [ 'Switch pos', 'active', 1 ],
               )
             ->generate();

      [download]
      The => after the first arguments look nice, especially since the first arguments are instance handles, and I use them as a hash key.

      In this example the arguments to anatrace really aren't mutators, they are constructors of sub-objects. They are waveforms being added to a scope display.

      update
      Is the problem that you perceive just with mutators, or does it also apply to sub-object constructors? Can you provide examples of acceptable method chaining, and contrast it with problematic method chaining?

      It should work perfectly the first time! - toma
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[d/l]

In Section Meditations