creating operands

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Re: creating operands by jdporter (Paladin) on Jul 13, 2006 at 16:58 UTC
This operator is called "defined-or". In Perl, it written as `//`; there is also a low-priority form, `err`. I believe these were introduced in core Perl as of 5.9.2. They are also in Perl 6. So, for your example, you'd do `$foo = $bar->id err $self->error('blah blah');` [download] We're building the house of the future together.	[reply] [d/l] [select]
Re^2: creating operands by diotalevi (Canon) on Jul 13, 2006 at 19:52 UTC
H. Merjin Brand also distributes patches against the 5.8.x series for this. They can be downloaded from his CPAN directory. ⠤⠤ ⠙⠊⠕⠞⠁⠇⠑⠧⠊	[reply]
Re: creating operands by ikegami (Patriarch) on Jul 13, 2006 at 17:49 UTC
Sorry, even overload doesn't allow you to create new operators. A source filter is really your only option here. The only other solution that comes to mind is the following: `sub definedor(&$) { defined($_[1]) ? $_[1] : $_[0]->() }` [download] However, the usage is uglier than your original code: `definedor { $self->error('blah blah')) } $foo = $bar->id; # Ugly defined($foo = $bar->id) or $self->error('blah blah')); # Better` [download]	[reply] [d/l] [select]
Re: creating operands by Tanktalus (Canon) on Jul 13, 2006 at 17:41 UTC
No. That was actually one of the issues that perl 6 is supposed to address: the ability to add new operators. All we have today are existing operators and functions. `sub definedor { defined $_[0] ? $_[0] : $_[1] }` [download] I think that's as good as you're going to be able to do before perl 5.9.2. Of course, if you want a more generic one that can take multiple inputs, sort of emulating `$a // $b // $c // ...`, you could do: `sub definedor { use List::Util qw(first); first { defined } @_ }` [download] and use it as `definedor($a, $b, $c, ...)` Of course, at this point, you almost may as well use the first function directly ;-)	[reply] [d/l] [select]
Re^2: creating operands by ikegami (Patriarch) on Jul 13, 2006 at 17:52 UTC
That doesn't work here. Your solution eliminates short-circuiting. Short-circuiting is crucial here since we only want `$self->error()` to execute when the LHS is undefined. Without short-circuiting, `$self->error()` will be called unconditionally. Short-circuiting is not even a bonus in the provided snippet. The OP uses or/definedor exclusively for its short-circuiting properties, since the return value of the or/definedor is discarded.	[reply] [d/l] [select]
Re: creating operands by Ieronim (Friar) on Jul 13, 2006 at 18:01 UTC
As you cannot create definedor operand and don't want to wait for Perl 5.10, emulate it (differs from previos variants, as assigns `$self->error` to `$foo`, what you maybe (???) want to do): `$foo = defined($bar->id) ? $bar->id : $self->error('blah blah');` [download]	[reply] [d/l] [select]
Re^2: creating operands by ikegami (Patriarch) on Jul 13, 2006 at 18:11 UTC
That's not equivalent. If you wanted to use the ternary operator, `defined($foo = $bar->id) or $self->error('blah blah');` would be equivalent to `defined($foo = $bar->id) ? undef : $self->error('blah blah');` `$foo = defined($bar->id) \|\| $self->error('blah blah');` would be equivalent to `$foo = defined($bar->id) ? $bar->id : $self->error('blah blah');` but that's not relevant here.	[reply] [d/l] [select]