Supported exporting closures with use() variables

[jasny]

Added the CLOSURE_USE_AS_VAR CLOSURE_SNAPSHOT_USE option to allow exporting closures with use() variables. Reflection is used to get the (current) value of these variables. These are exported by the exporter, parsed and inserted as statements.

Example

$planet = 'world';
echo VarExporter::export([
    'callback' => function() use ($planet) {
        return 'Hello, ' . $planet . '!';
    }
], VarExported::CLOSURE_SNAPSHOT_USE);

[
    'callback' => function () {
        $planet = 'world';
        return 'Hello, ' . $planet . '!';
    }
]

Added ClosureExporter::getParser() method, not to create multiple parsers for exporting a single closure.

[BenMorel]

Hi, this feature looks great, thank you!

A few questions:

• What happens if the use statement is a reference? i.e. use (& $foo)? I guess we should throw an exception (and document this)?
• maybe CLOSURE_USE_AS_VAR would be better named CLOSURE_SNAPSHOT_USE?

[BenMorel]

I didn't know that getStaticVariables() returned use statements, too. Is this documented anywhere? The manual doesn't say anything about it, so this makes me a bit chilly to rely on it!

This also made me curious: what happens if you have both a use statement and a static variable with the same name? It looks like use wins, so at least we should be safe here:

https://3v4l.org/jbGIf

[jasny]

getStaticVariables() returns op_array.static_variables. This is intended for variables bound with static, but closures also use this array for the use variables.

I asked @nikic; This is an implementation detail and might be changed in the future (PHP 8). However, it should always be possible to get these vars using reflection. So if it's changed, a method like ReflectionFunction::getUseVariables() would be added.

[BenMorel]

Alright, with good unit tests we should be covered anyway. Maybe it's time to start testing against nightly (with allow_failures), so that we know right away if this implementation detail changes?

[jasny]

I don't think we should do anything special with referenced use variables like use (& $foo) since varexporter always ignores references. Eg;

$foo = "Foo";
$var = ['x' => &$foo, 'y' => &$foo];

VarExporter::export($var);

[
    'x' => 'Foo',
    'y' => 'Foo'
]

Naming the option CLOSURE_SNAPSHOT_USE also suggests this behavior.

[BenMorel]

I don't think we should do anything special with referenced use variables like use (& $foo) since varexporter always ignores references.

Makes sense, I guess. I'm never really comfortable with references.

[BenMorel]

Awesome work, thank you! 👍 Let's move on to #8.

[BenMorel]

Released in 0.3.1 🚀