use CGI::Application; imports the symbols from CGI::Application (if any) everytime it's executed.
use CGI::Application qw( );, on the other hand, is just a require that occurs at compile-time.
use base doesn't seem to have much overhead.

If I have 10 calls to 'use' in various modules (same namespace definition).. how much of a hit is that for the interpreter?

Benchmark it. It's the only way to know.

In reply to Re: Do multiple calls to 'use X' abuse the compiler? by ikegami
in thread Do multiple calls to 'use X' abuse the compiler? by leocharre

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