Will Shaver Will Shaver - 3 months ago 14
PHP Question

Implicit Type Conversion for PHP Classes?

Is there a way to tell the php complier that I want a specific implicit conversion from one type to another?

A simple example:

class Integer
{
public $val;
}

function ExampleFunc(Interger $i){...}

ExamFunc(333); // 333 -> Integer object with $val == 333.


[edit]... someone asked for an example. Here's an example from c#. This is a boolean type that changes value after it has been accessed once.

/// <summary>
/// A Heisenberg style boolean that changes after it has been read. Defaults to false.
/// </summary>
public class hbool
{
private bool value;
private bool changed = false;

public hbool()
{
value = false;
}

public hbool(bool value)
{
this.value = value;
}

public static implicit operator bool(hbool item)
{
return item.Value;
}

public static implicit operator hbool(bool item)
{
return new hbool(item);
}

public bool Value
{
get
{
if (!changed)
{
value = !value;
changed = true;
return !value;
}
return value;
}
}

public void TouchValue()
{
bool value1 = Value;
}

public static hbool False
{
get { return new hbool(); }
}

public static hbool True
{
get { return new hbool(true); }
}
}

[Test]
public void hboolShouldChangeAfterRead()
{
hbool b = false;
Assert.IsFalse(b);
Assert.IsTrue(b);
Assert.IsTrue(b);
hbool b1 = false;
Assert.IsFalse(b1);
Assert.IsTrue(b1);
Assert.IsTrue(b1);
hbool b2 = true;
Assert.IsTrue(b2);
Assert.IsFalse(b2);
Assert.IsFalse(b2);
bool b3 = new hbool();
Assert.IsFalse(b3);
Assert.IsFalse(b3);
Assert.IsFalse(b3);
}

Answer

Long answer:

I think it is very difficult (read impossible) for PHP to do an implicit conversion in this case.

Remember: the fact that you call your class Integer is a hint to the human reader of the code, PHP does not understand that it actually is used to hold an integer. Also, the fact that it has an attribute called $val is a hint to a human reader that it should probably contain the value of your integer. Again PHP does not understand your code, it only executes it.

At some point in your code you should do an explicit conversion. It might be possible that PHP has some nice syntactig sugar for that, but a first attempt would be something like:

class Integer
{
  public $val;

  function __construct($val) { $this->val = $val; }
}

function ExampleFunc($i){
    if (is_numeric($i)) { $iObj = new Integer($i); }
    ...
}

ExamFunc(333); // 333 -> Integer object with $val === 333.

This is not as cool as you would like it, but again, it is possible that PHP has some syntactic sugar that will hide the explicit conversion more or less.

Short version:

In one way or another, you will need an explicit conversion