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Message from discussion Binary pattern matching and optimization
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Vance Shipley  
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 More options Nov 24 2008, 1:08 pm
From: Vance Shipley <van...@motivity.ca>
Date: Mon, 24 Nov 2008 13:08:32 -0500
Local: Mon, Nov 24 2008 1:08 pm
Subject: [erlang-questions] Binary pattern matching and optimization
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I would like to have a function like this:

        foo(<<_:Offset/binary, Foo:8, _/binary>>, Offset) ->
                bar(Bin, Foo).

Unfortunately that doesn't work:

        Eshell V5.6.5  (abort with ^G)
        1> compile:file(codec).
        ./codec.erl:15: variable 'Offset' is unbound
        error

I don't understand why the first version can't work but
neither do I understand much about writing compilers.

So instead I do this:

        foo(Bin, Offset) ->
                <<_:Offset/binary, Foo:8, _/binary>> = Bin,
                bar(Bin, Foo).

This works fine of course but now I am trying to understand
the meaning of this (optional) compiler warning:

        Warning: INFO: using a matched out sub binary will prevent
        delayed sub binary optimization

How should I interpret this warning?

        -Vance
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