Perlbuzz news roundup for 2014-09-15

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Template Toolkit’s DEFAULT directive does not short-circuit

Template Toolkit’s DEFAULT does not do short-circuit evaluation like you might think it would.
If you have
[% DEFAULT foo = user.calculate_foo; %]
Then the results of the method call `user.calculate_foo` are assigned to `foo`, unless `foo` already has a true value.
However, whether or not foo already has a true value, `user.calculcate_foo` is always invoked.
You might expect the code to look like this:
$foo = $user->calculate_foo() unless $foo;
But it’s really like this;
$temp = $user->calculate_foo();
$foo = $temp unless $foo;
So, if `user.calculate_foo` is an expensive function that you don’t want to invoke unless you have to, you’ll have to resort to an explicit `IF` block:
IF !foo;
foo = user.calculate_foo;
END
It’s also worth noting that `DEFAULT` is not for checking if a variable is set, but for checking if it is true.

Perlbuzz news roundup for 2014-08-11

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Perlbuzz news roundup for 2014-07-14

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Perlbuzz news roundup for 2014-06-06

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Perlbuzz news roundup for 2014-05-19

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Perlbuzz news roundup for 2014-05-05

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Perlbuzz news roundup for 2014-04-21

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Perlbuzz news roundup for 2014-03-31

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Perlbuzz news roundup for 2014-03-17

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