PHP Mapping for Parameters and Return Values

In Parameters

The PHP mapping for in parameters guarantees that the value of a parameter will not be changed by the invocation.

Here is an interface with operations that pass parameters of various types from client to server:

struct NumberAndString
{
    int x;
    string str;
}

sequence<string> StringSeq;

dictionary<long, StringSeq> StringTable;

interface ClientToServer
{
    void op1(int i, float f, bool b, string s);
    void op2(NumberAndString ns, StringSeq ss, StringTable st);
    void op3(ClientToServer* proxy);
}

The Slice compiler generates the following methods for this definition:

function op1($i, $f, $b, $s, $context=null);
function op2($ns, $ss, $st, $context=null);
function op3($proxy, $context=null);

Given a proxy to a ClientToServer object, the client code can pass parameters as in the following example:

$p = ...                                 // Get proxy...

$p->op1(42, 3.14, true, "Hello world!"); // Pass simple literals

$i = 42;
$f = 3.14;
$b = true;
$s = "Hello world!";
$p->op1($i, $f, $b, $s);                 // Pass simple variables

$ns = new NumberAndString;
$ns->x = 42;
$ns->str = "The Answer";
$ss = array("Hello world!");
$st = array();
$st[0] = $ns;
$p->op2($ns, $ss, $st);                  // Pass complex variables

$p->op3($p);                             // Pass proxy

Out Parameters

Out parameters are passed by reference. Here is the same Slice definition we saw earlier, but this time with all parameters being passed in the out direction:

struct NumberAndString
{
    int x;
    string str;
}

sequence<string> StringSeq;

dictionary<long, StringSeq> StringTable;

interface ServerToClient
{
    int op1(out float f, out bool b, out string s);
    void op2(out NumberAndString ns,
             out StringSeq ss,
             out StringTable st);
    void op3(out ServerToClient* proxy);
}

The PHP mapping looks the same as it did for the in parameters version:

function op1($i, $f, $b, $s, $context=null);
function op2($ns, $ss, $st, $context=null);
function op3($proxy, $context=null);

Given a proxy to a ServerToClient object, the client code can receive the results as in the following example:

$p = ...                 // Get proxy...
$p->op1($i, $f, $b, $s);
$p->op2($ns, $ss, $st);
$p->op3($stcp);

Note that it is not necessary to use the reference operator (&) before each argument because the Ice runtime forces each out parameter to have reference semantics.

Parameter Type Mismatches

Ice validates the arguments to a proxy invocation at runtime and reports any type mismatches as a InvalidArgumentException exception.

Null Parameters

Some Slice types naturally have "empty" or "not there" semantics. Specifically, sequences, dictionaries, and strings all can be null, but the corresponding Slice types do not have the concept of a null value. To make life with these types easier, whenever you pass null as a parameter or return value of type sequence, dictionary, or string, the Ice runtime automatically sends an empty sequence, dictionary, or string to the receiver.

This behavior is useful as a convenience feature: especially for deeply-nested data types, members that are sequences, dictionaries, or strings automatically arrive as an empty value at the receiving end. This saves you having to explicitly initialize, for example, every string element in a large sequence before sending the sequence in order to avoid a run-time error. Note that using null parameters in this way does not create null semantics for Slice sequences, dictionaries, or strings. As far as the object model is concerned, these do not exist (only empty sequences, dictionaries, and strings do). For example, it makes no difference to the receiver whether you send a string as null or as an empty string: either way, the receiver sees an empty string.

Optional Parameters

Optional parameters use the same mapping as required parameters. The only difference is that \Ice\None can be passed as the value of an optional parameter or return value. Consider the following operation:

optional(1) int execute(optional(2) string params, out optional(3) float value);

A client can invoke this operation as shown below:

$i = $proxy->execute("--file log.txt", $v);
$i = $proxy->execute(\Ice\None, $v);
 
if($v != Ice_Unset)
{
    echo "value = " . $v . "\n";
}

A well-behaved program must always compare an optional parameter to \Ice\None prior to using its value. Keep in mind that the \Ice\None marker value has different semantics than null. Since null is a legal value for certain Slice types, the Ice runtime requires a separate marker value so that it can determine whether an optional parameter is set. An optional parameter set to null is considered to be set.