Re^4: expression which does nothing

It's possible to avoid the warning by using 1 (or 0) instead of 42.

>perl -w -e 42
Useless use of a constant in void context at -e line 1.

>perl -w -e 1
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It's a special case to allow 1 while ...;.

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Re^5: expression which does nothing by bart (Canon) on Dec 27, 2006 at 11:27 UTC
Not just that. It's also to allow the bare `1;` at the end of modules to make it end in a true value, without a complaint under `perl -c Foo.pm`. Note that no true value at the end of a module, whatever you choose, causes a complaint under normal cicrumstances, actually because a module is loaded in scalar context. As a test: I saved this little module as "Temp.pm" in the current directory: `# Temp.pm package Temp; printf "Context = %s\n", defined wantarray ? 0+wantarray : 'undef'; # true value, but may cause warning: "nothing";` [download] This command line makes it work without warning: `perl -lib=. -MTemp -we1` [download] Result: Context = 0 But with `perl -wc`, you do get a warning: `perl -wc Temp.pm` [download] Useless use of a constant in void context at Temp.pm line 3. Temp.pm syntax OK Replace the string `"nothing"` with `1`, and you're fine: Temp.pm syntax OK	[reply] [d/l] [select]

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Re^5: expression which does nothing
by bart (Canon) on Dec 27, 2006 at 11:27 UTC

1;

perl -c Foo.pm

Note that no true value at the end of a module, whatever you choose, causes a complaint under normal cicrumstances, actually because a module is loaded in scalar context.

As a test: I saved this little module as "Temp.pm" in the current directory:

# Temp.pm
package Temp;
printf "Context = %s\n", defined wantarray ? 0+wantarray : 'undef';
# true value, but may cause warning:
"nothing";
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perl -lib=. -MTemp -we1
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Context = 0

But with perl -wc, you do get a warning:

perl -wc Temp.pm
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Useless use of a constant in void context at Temp.pm line 3.
Temp.pm syntax OK

Replace the string "nothing" with 1, and you're fine:

Temp.pm syntax OK

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