A less-distracting example might be a ball with mass, velocity, and momentum (calculate the third given two). I still think reaching for a lazy-building pile of Moose goop is wrong, since it's way easier to just have a cache: 
sub momentum {
    my $self = shift;
    $self->{momentum} //= $self->{mass} * $self->{velocity};
}

[download]
but at least this may let people focus on the idea.

In reply to Re^4: Idea: Moose Mutal Coercion by educated_foo
in thread Idea: Moose Mutual Coercion by k0st

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