[Libguestfs] [PATCH] Export inspect_linux_kernel in Lib.pm

Jim Meyering jim at meyering.net
Wed Aug 19 14:18:02 UTC 2009


Matthew Booth wrote:
> diff --git a/perl/lib/Sys/Guestfs/Lib.pm b/perl/lib/Sys/Guestfs/Lib.pm
...
> @@ -1551,10 +1552,19 @@ sub _check_for_kernels
...
>                  # Check the kernel was recognised
>                  if(defined($kernel)) {
> +                    # Put this kernel on the top level kernel list
> +                    my $kernels = $os->{kernels};
> +                    if(!defined($kernels)) {
> +                        $kernels = [];
> +                        $os->{kernels} = $kernels;
> +                    }
> +                    push(@$kernels, $kernel);
> +

Hi Matt,

It took me too long to see what was being done above,
so I rewrote it in a way that I found easier to read:

How about this?

diff --git a/perl/lib/Sys/Guestfs/Lib.pm b/perl/lib/Sys/Guestfs/Lib.pm
index dfa79af..2acdec6 100644
--- a/perl/lib/Sys/Guestfs/Lib.pm
+++ b/perl/lib/Sys/Guestfs/Lib.pm
@@ -1558,12 +1558,8 @@ sub _check_for_kernels
                 # Check the kernel was recognised
                 if(defined($kernel)) {
                     # Put this kernel on the top level kernel list
-                    my $kernels = $os->{kernels};
-                    if(!defined($kernels)) {
-                        $kernels = [];
-                        $os->{kernels} = $kernels;
-                    }
-                    push(@$kernels, $kernel);
+                    $os->{kernels} ||= [];
+                    push(@{$os->{kernels}}, $kernel);

                     $config{kernel} = $kernel;


The ||= operator may look odd, but it's another of these idiom things.
Once you see it a few times, then "get it", and start using it,
you'll never go back.

Which would you prefer to read/maintain?  This:

    # Ensure the array-ref is initialized.
    if (!defined $some_long_name->[$some_complicated_expression]) {
        $some_long_name->[$some_complicated_expression] = [];
    }

    # Append to it.
    ...

or this:

    # Ensure the array-ref is initialized.
    $some_long_name->[$some_complicated_expression] ||= [];

    # Append to it.
    ...




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