Function passed to imp.wakeup by value or by reference

Squirrel Code
1

This is partially a question and partially an example i would like to offer. I was trying to build a wakeup function that I could change with other code. I wanted the imp, when woken to perhaps run a different function than originally planned in the wakeup call. I think this technique is a little related to C function pointers which do not exist in this system.

I found that if I referenced a function directly I could not change it. If I wrap the function inside another function then I can change it. My example below is an attempt to show that.

My question is whether anyone thinks this is a bad technique? is there a better one? I am not sure how I would use this; I am just trying to feel out the language.

`

function testdefine(){
server.log(“test define”);
}

function testSecond(){
server.log(“test Second”);
}

function testFinal(){
server.log(“test Final”);
}

function aChangingFunction(){

placeholder();

}

placeholder <- testdefine;//testdefine is a function

placeholder(); //prints "test define"
aChangingFunction(); //prints “test define”

placeholder = testSecond;

server.log (".");
aChangingFunction(); //prints “test Second"
placeholder(); //prints “test Second"
server.log (”.”);

function changeit()
{
placeholder=testFinal;
server.log(“changed”);
}

imp.wakeup(7, placeholder); //will print “test Second”

placeholder=testdefine;

imp.wakeup(37,placeholder);//at the time is testdefine, doesn’t change

imp.wakeup(15,function() {changeit(); imp.wakeup(5,placeholder);});

imp.wakeup(60,aChangingFunction);

server.log(imp.getmemoryfree());
`

output is :

2/19/2013 12:47:00 PM: Device booting
2/19/2013 12:47:00 PM: test define
2/19/2013 12:47:00 PM: test define
2/19/2013 12:47:00 PM: .
2/19/2013 12:47:00 PM: test Second
2/19/2013 12:47:00 PM: test Second
2/19/2013 12:47:00 PM: .
2/19/2013 12:47:00 PM: 56796
2/19/2013 12:47:07 PM: test Second
2/19/2013 12:47:16 PM: changed
2/19/2013 12:47:21 PM: test Final
2/19/2013 12:47:39 PM: test define
2/19/2013 12:48:04 PM: test Final

The second-to-last printing of “test define” is something I thought might be “test Final” because I change what placeholder ‘points’ to.

2

Thanks for sharing.
Seems to be useable as a kind of void function pointer.
Will need some hands-on to gat a better feel for it, though.

3

I suspect the reference to the function to call back is taken at the time imp.wakeup is called, which explains the behavior. It’s not the variable, it’s the thing to execute.

4

Thanks Hugo, I see it now.

Here is a cleaned up example that I think shows how this works.

`
function testFirst(){server.log(“t First”);}

function testSecond(){server.log(“t Second”);}

function testFinal(){server.log(“t Final”);}

placeholder <- testFirst;//testFirst is a function

function aChangingFunction(){
placeholder();
}

placeholder(); //prints "t First"
aChangingFunction(); //prints “t First”

placeholder = testSecond;

aChangingFunction(); //prints "t Second"
placeholder(); //prints “t Second”

function changeit()
{
placeholder=testFinal;
server.log(“changed to testFinal”);
}

placeholder=testFirst;

server.log(".");
placeholder();
server.log("-");

imp.wakeup(5,changeit);
imp.wakeup(10,function() {placeholder();});
imp.wakeup(15,placeholder);
imp.wakeup(20,aChangingFunction);`

prints this:

6:07:59 AM: Device booting
6:07:59 AM: t First
6:07:59 AM: t First
6:07:59 AM: t Second
6:07:59 AM: t Second
6:07:59 AM: .
6:07:59 AM: t First
6:07:59 AM: -
6:08:04 AM: changed to testFinal
6:08:10 AM: t Final
6:08:15 AM: t First
6:08:21 AM: t Final

so in the end, pretty elementary.