# Cannot use const within try block

- Thread: https://externals.io/message/74263
- Original archive: https://news-web.php.net/php.internals/74263
- Started by Alain Williams on 2014-05-16T14:44:08+00:00
- Messages: 2
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## #74263 — Alain Williams — 2014-05-16T14:44:08+00:00

URL: https://externals.io/message/74263#74263

The code below gives me: PHP Parse error:  syntax error, unexpected `T_CONST` in ...

try {
    const XXX = 12;

    echo "XXX = " . XXX . "\n";

}catch (ErrorException $e) {
    echo "error {$e->getMessage()}\n";
}

It works if I put the 'cost' before/outside the 'try'.

It also works if I replace the const line by:

    define('XXX', 'twelve');

or

    include "testdef.php";

where testdef.php contains:

    const XXX = 12;

I cannot find this behaviour documented.

a) If there is no good reason for this restriction - can it be removed.

or

b) If there is good reason for it can this be documented.

Regards

-- 
Alain Williams
Linux/GNU Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256  http://www.phcomp.co.uk/
Parliament Hill Computers Ltd. Registration Information: http://www.phcomp.co.uk/contact.php
#include <std_disclaimer.h

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## #74264 — Chris Wright — 2014-05-16T15:08:59+00:00

URL: https://externals.io/message/74263#74264 · In reply to: #74263

> The code below gives me: PHP Parse error:  syntax error, unexpected `T_CONST` in ...
>
> try {
>     const XXX = 12;
>
>     echo "XXX = " . XXX . "\n";
>
> }catch (ErrorException $e) {
>     echo "error {$e->getMessage()}\n";
> }
>
> It works if I put the 'cost' before/outside the 'try'.
>
> It also works if I replace the const line by:
>
>     define('XXX', 'twelve');
>
> or
>
>     include "testdef.php";
>
> where testdef.php contains:
>
>     const XXX = 12;
>

Defining constants using const is handled at compile time. Because of
this, it cannot be dependent on branches that are only processed at
run time. When you include a file, this creates a new "compile-time"
for the included file, so the operation succeeds.

 `define()` is a regular function call evaluated at run time.

As such if you want a constant defined conditionally then you'll need
to use `define()`

> I cannot find this behaviour documented.
>
> a) If there is no good reason for this restriction - can it be removed.
>
> or
>
> b) If there is good reason for it can this be documented.

This behaviour is documented; to quote the note at http://php.net/const

"As opposed to defining constants using `define()`, constants defined
using the const keyword must be declared at the top-level scope
because they are defined at compile-time. This means that they cannot
be declared inside functions, loops or if statements."

I will update the note shortly to include try/catch blocks.

Thanks, Chris