#21 "Pass by reference"

[Haravikk]

Okay, obviously not a real-thing, but this relates to inlined functions. Basically it would be cool if we could provide a hint specifying function parameters which should /not/ be copied when inlined. For example, this function:

string doSomething(string msg) {
return msg;
}

myMsg = doSomething(myMsg);

Ignoring optimisation could end up being inlined like:

string msg0 = myMsg;
string ret0 = msg0;
myMsg = ret0;

Obviously this is only an example case to illustrate the point, but it's a bit wasteful. If however we were able to specify that it's okay to just pass in the raw value, then the need for copying in this way could be removed.

[None]

Are you suggesting that the sequence:

string msg0 = myMsg;
string ret0 = msg0;
string myMsg = ret0;

actually copies the strings, rather than references to the strings? I don't believe this is the case, as strings in LSL are immutable.

[Haravikk]

I'm just trying to illustrate this with a trivial case. A more involved one might be:

string msg0 = msg;
msg0 = llDeleteSubString(msg0, 0, 0);
msg = ms0;

Immediately before the line "msg = msg0;" there are now two-strings, almost the same size, whereas ideally there'd only be one, with the originally value of msg becoming orphaned for garbage-collection.

Thinking about it it may be better overall if the compiler was able to detect that a variable is being assigned a value from a function to which it was passed as an argument, thus meaning there is no need for a copy to be created as any change to the variable itself won't matter. However, pass-by-reference may be more useful in more complex cases, for example if I wanted to have an inline function capable of directly modifying any global variable I pass to it, for example:

// pragma inline
doSomethingToList(list l) {
// Does something to list
}

doSomethingToList(myList);
doSomethingToList(myOtherList);