How to resolve non-existant index in array?

Question

I have my own class for templates. In this class, I replace string likes {NEXT_PAGE} to

<?php echo $tpl->vars["NEXT_PAGE"]; ?>

But sometimes happen, that this index doesn't exists.

I found topic PHP: is_array on $arr['key'] with non existing 'key' and I know how to check if some index exists.

My question is, what is better to improve performance.

1. Always check if index exist and if yes, print it
2. Just print it without checking if index exists.

First solution is great, no warning, no errors, no notices, but I go through array twice, first time to check it, second time to print it. Need more CPU time.

Second solution just try to find it, if it exists print it, otherwise print empty string, it's OK for me, and warnings I can disable by error_reporting

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So what is better? I think that second solution with disabling warnings. PHP always have to check if index exists, but when I check it too, it is checked twice. Am I right?

Just to be clear, accessing to index which doesn't exists is max 3% of all accessing to this array.

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Example I have a form, where I put back login name, if pass is incorrect. When I replace {LOGIN_NAME} by <?php echo $tpl->vars["LOGIN_NAME"]; ?> I save this new file like a PHP script, so later I just run this, no replacing again!

So my compiled script is something like this

<form ...>
<input type="login" ... value="<?php echo $tpl->vars["LOGIN_NAME"] ?>" />
(pass etc...)
</form>

So when someone visit this page for the first time LOGIN_NAME isn't set, PHP can't print anything but it's OK, field is still empty. If form is send, script add to LOGIN_NAME sent login name and then field isn't empty.

Answer 1

You are currently looping through pattern matches in a file and then replacing the matches with the corresponding template var, if it is set.

Why don't you come at the problem from the other side?

Loop through your template vars and replace pattern matches in the file. Then, afterwards, replace any remaining pattern matches with the empty string.

foreach ($tpl->vars as $key => $val) {
    $template = str_replace("{$key}", $val, $template);
}
$template = preg_replace('/{(.+?)}/', '', $template);

Update: Since you want to write a php string into the template instead of the actual value, the code would look like this:

foreach ($tpl->vars as $key => $val) {
    $template = str_replace("{$key}", "<?php echo \$tpl->vars['$key']; ?>", $template);
}
$template = preg_replace('/{(.+?)}/', '', $template);

Then $template would contain a string which you write to the cache. The principle is the same.

Answer 2

Is your system performance critical? How many lookups will you perform per second?

A post on how isset() is faster than array_key_exists(). http://ilia.ws/archives/247-Performance-Analysis-of-isset-vs-array_key_exists.html

Think about what does it mean in terms of design to have or not have this key in the array. Should it always be there? Is the model valid in each case?

My current understanding is that the lookup is required.

Answer 3

You could put @ in front of your echo statement, which would suppress any errors. There are probably also other ways of writing a template engine that don't require array access in this way (perhaps using a custom object instead, or the extract() function), but the @ trick seems simplest here.

Answer 4

you can check if an index of a variable exists with the isset function:

if (isset($tpl->vars["NEXT_PAGE"]))
{
}