The syntax my Dog $brain declares that $brain is a Dog, and therefore everything that can be done with $brain has to be something that a Dog can do.

These are compile-time tests on the container $brain.

There is no runtime check in Perl 5 about whether the value put into $brain actually is a Dog. And the following line cannot be construed as a code error - after all nothing stops someone from making a class that inherits from both Dog and Brain!

In reply to Re^4: use fields; # damnit by tilly
in thread use fields; # damnit by nothingmuch

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