pub fn new(callable: &'a Zval) -> Result<Self> {
        if callable.is_callable() {
            Ok(Self(OwnedZval::Reference(callable)))
        } else {
            Err(Error::Callable)
        }
    }
Attempts to create a new [`ZendCallable`] from a zval.

# Parameters

* `callable` - The underlying [`Zval`] that is callable.

# Errors

Returns an error if the [`Zval`] was not callable.
src/types/callable.rs