http://qs1969.pair.com?node_id=377570

kryten has asked for the wisdom of the Perl Monks concerning the following question:

I have a testing routine which, as part of the test, calls a function in a way that generates a warning message. I am expeting this warning message and would like to supress it in order to have clean test output. However I only want to supress the warning message for this instance of the function call and I want to keep any other error messages that might occour.

I have tried using the 'no warnings qw/type/' pragma but have run into what seems to be a block nesting problem. According to perllexwarn the warnings pragma works on a block level which is fine. My problem seems to be when trying to control runtime warnings the scope doesn't work as I'm expecting: 
#!/bin/perl 
use warnings::register;
use warnings;

printf( "Perl Version: %vd\n",$^V);
test_warnings();

sub GenerateWarning {
    warn  "warnings are ",
            warnings::enabled() ? "" : "not ",
            "enabled\n";
}

sub test_warnings {
    no warnings;
    GenerateWarning();
    AnotherSub();
}

sub AnotherSub {
    GenerateWarning();
}

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Produces the output: 
Perl Version: 5.6.1
warnings are not enabled
warnings are enabled

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What I would like is for warnings to be not enabled both times. Is there a way to do what I want to do? Should I be doing this a different way?

Replies are listed 'Best First'.
Re: Nested runtime warning disabling
by ccn (Vicar) on Jul 26, 2004 at 20:46 UTC

    warnings have lexical scope, so 

    no warnings;

sub test_warnings {
    GenerateWarning();
    AnotherSub();
}

sub AnotherSub {
    GenerateWarning();
}

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    also, may be this code be useful for you 

    sub test_warnings {
    local $SIG{__WARN__} = sub {};
    GenerateWarning();
    AnotherSub();
}

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[select]
      The problem with moving the 'no warnings' outside the test_warnings sub is that I will not get warnings when I call: 
      sub another_test {
   AnotherSub();
}

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      The local signal handler might work if I can just catch the class of error I'm trying to supress and 'pass through' everything else as normal.
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Re: Nested runtime warning disabling
by gaal (Parson) on Jul 26, 2004 at 20:42 UTC
    Hackish, but you could use Hook::LexWrap to surround your GenerateWarning() with a wrapper that does no warnings;.
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      Thanks. I tried out Hook::LexWrap 
      use Hook::LexWrap;

sub test_warnings {
    my $lexical = wrap 'GenerateWarning', pre => sub { no warnings };
    GenerateWarning();
    AnotherSub();
}

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      This does produce the result I was looking for, but I agree it is a little hackish.

      Does anyone have a more elegant solution?

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