(Possible) Breaking change: local variables references inside nested function definitions

orange

@d-healey said in (Possible) Breaking change: local variables references inside nested function definitions:

@orange This problem was always there

My previous projects can't be opened with the latest develop branch.
But if I modify the local variables as var it works. So this issue is a new one.

d.healey

@orange

But if I modify the local variables as var it works. So this issue is a new one.

No it's an old issue, but now there is a new error so it might cause problems with opening old projects.

You don't need to change all locals to var - in fact that is a really bad idea. You only need to change the ones that are in nested functions. And I recommend not changing them to var because that pollutes the scriptwide namespace, I think it's better to create a reg object at the top of each namespace that can be used to hold the values - should I make a video about this?

orange

@d-healey Ok I will try with reg thanks.

So only modifying the places that the Hise gives the warnings is enough? Or even Hise doesn't give warnings, I should modify all nested functions?

d.healey

@orange

Ok I will try with reg thanks.

Just 1 reg at the top of the namespace.

I should modify all nested functions

Only nested functions (not inline functions) that are affected by this issue. The issue is that the variables go out of scope in certain circumstances. For example if you are calling something like Engine.showYesNoWindow() The callback function that you pass to that function will be triggered after any local variables have already been destroyed.

So it's basically anywhere you are using a callback function. A few examples would be:

Engine.showYesNoWindow()
Server.downloadFile()
File.extractZipFile()
FileSystem.browse()
FileSystem.browserForDirectory()

A Former User

I am just trying to understand the case about what to do here. I have a script like below and I am getting Cannot define local variables outside of inline functions or callbacks. error in Hise - the current develop branch.

inline function onMYGENERICFUNCControl(component, value)
{
      local myLocalOne = Engine.getSystemTime();  
      local myLocalTwo = Engine.getVersion();
      local myLocalThree = Engine.showYesNoWindow(); 
        
    if(value)
    {
      // Execute a function

    }


    else
    {
      // Execute a function

    }
};

Content.getComponent("MYGENERICFUNC").setControlCallback(onMYGENERICFUNCControl);

So Should I transform the local variables with namespace & reg combination like this? Is this an effective usage?

namespace myNamespaceFunc
{	
	reg myLocalOne;
	reg myLocalTwo;
	reg myLocalThree;
			
	inline function onMYGENERICFUNCControl(component, value)
	{	
	    myLocalOne = Engine.getSystemTime();  
	    myLocalTwo = Engine.getVersion();
	    myLocalThree = Engine.showYesNoWindow(); 
	        	
	    if(value)
	    {
	      // Execute a function
	
	    }
	
		
	    else
	    {
	      // Execute a function
	
	    }
		
	};
		Content.getComponent("MYGENERICFUNC").setControlCallback(onMYGENERICFUNCControl);
	
};

d.healey

@Steve-Mohican You shouldn't be getting an error there, that is an inline function. Are you sure that is where the error is being generated?

A Former User

@d-healey Yes I am getting that error exactly there.

I am also using a Server.callWithGET() inside the if statement and using these 3 variables in the if statement but I just trimmed the code to make it more clean

d.healey

@Steve-Mohican Aha now it's making more sense. The Server.callWithGET() function takes a callback function as its last parameter. Within this inner function you cannot declare local variables or use local variables declared outside of this function.

For this you should make a reg object at the top of your namespace called nest, and use this object in place of your local variables. For example:

Don't do this

namespace myNamespace
{
    inline function myFunc()
    {
        local myVar1 = 10;
        local myVar2 = 20;

        Server.callWithGET("google.com", {}, function()
        {
            Console.print(myVar1); // myVar1 doesn't exist here so you will get an error
        });
    }
}

Do this:

namespace myNamespace
{
    reg nest = {};

    inline function myFunc()
    {
        nest.myVar1 = 10;
        nest.myVar2 = 20;

        Server.callWithGET("google.com", {}, function()
        {
            Console.print(nest.myVar1);
        });
    }
}

@Christoph-Hart As a longer term solution is it possible to do something behind the scenes that allows local variables to exist within the inner functions? Maybe internally they are converted to reg variables...

A Former User

@d-healey Wow, very different solution. Thank you for the suggestion, I will check!

d.healey

@Christoph-Hart said in (Possible) Breaking change: local variables references inside nested function definitions:

In your case you might get away with just changing local to var for the origin definition.

I'm finding this approach is causing problems in other functions that use the same variable names. My nest solution is still working fine but it's ugly code. Is there a possibility of some syntactic sugar being added to HISE so that we can use the word local in these scenarios and internally HISE will treat them as children of a reg variable, just like I'm doing with my reg nest method?

Edit: I just realised I asked this already :p

andioak

@Christoph-Hart @d-healey It's been a while for me here at the Hise forums, so please correct me if I'm wrong, but isn't one important issue the fact that we're using "inline" functions?

Perhaps we could be using normal functions (not "inline") for things that are asynchronous in nature, such as the fetching of files through the FileSystem.browse() object. If the "inline" is the issue that makes the local variables go out of scope, when the stack is not synchronously executed as per the inline function specification. (if I'm getting that bit right :beaming_face_with_smiling_eyes: )

After all, the inlining of functionality is for things that are very sensitive in timing, real-time stuff for audio and such things. This is not going to run in the same threads as the audio streaming, right?

Otherwise, the "asynchrounous:ness" of the file browser could perhaps be explained a bit, I would love some info on that. Looking at the docs atm :)

(a novice at C++ at best still :) )

d.healey

@andioak said in (Possible) Breaking change: local variables references inside nested function definitions:

@Christoph-Hart @d-healey It's been a while for me here at the Hise forums, so please correct me if I'm wrong, but isn't one important issue the fact that we're using "inline" functions?

The particular issue in this thread is when you use a non-inline function within and inline function. This is often the case when using things like the file browser which requires a callback function as a parameter.

andioak

@d-healey said in (Possible) Breaking change: local variables references inside nested function definitions:

The particular issue in this thread is when you use a non-inline function within and inline function. This is often the case when using things like the file browser which requires a callback function as a parameter.

@d-healey Yes, I know. But why use an inline function to begin with in the case of the file browser? (or anything asynchronous in nature) Is not better to use a normal function in the cases that require asynchronous behaviour?

d.healey

@andioak You could use a normal function but the problem of scope would remain.

Christoph Hart

In C++ there is a concept where you can pass on certain variables to a local function (google lambda capture for more info), so maybe I can hack around again and frankenstein that feature into HiseScript…

Christoph Hart

You could use a normal function but the problem of scope would remain.

Oh but this is wrong (at least according to my understanding of the issue). Normal functions do have a local scope that will not overwrite the global variable, but inline functions don't:

var x = 100;

inline function overwriteRootVariable()
{
	var x = 90;
}

function dontOverwriteRootVariable()
{
	var x = 1000;
}

overwriteRootVariable();
dontOverwriteRootVariable;

Console.print(x);

d.healey

@Christoph-Hart Aha that's good to know. In that case I assume a callback function within a normal function still won't have access to the outer function's variables, correct? I like the lambda idea.

Christoph Hart

@d-healey Ah yes, that's true, just checked.

I've added the explicit capture syntax. It looks a bit weird coming from JS, but is inspired from the big mighty C++ again. It only works with anonymous functions so all you need to do is to put a list of all local variables and parameters between the function keyword and the parameter list

function [variables] (parameters)
{
   body;
}

Example usage:

inline function testScope(p)
{
	local x = 900;
	
	Engine.showYesNoWindow("Show local value", "Click OK", function [p, x](ok)
	{
		Console.print(p);
		Console.print(x);
	});
};

function testScope2(p)
{
	var x = 200;
	
	Engine.showYesNoWindow("Show local var", "Click OK", function [p, x](ok)
	{
		Console.print(p);
		Console.print(x);
	});
};


testScope(10);
testScope2(19);

~~There are still a few limitations (eg. the captured values will be overwritten by the last call),~~ but let me know if that helps. Edit: removed this limitation :)

d.healey

@Christoph-Hart Fast work! I'll play around with this tomorrow and let you know if I hit any issues, but look like a good improvement to me.

andioak

@Christoph-Hart Great. Looks like the C++ examples I just read about on the Lambda / Lambda Capture pages.

As I understand it, C++ did not have any capacity to declare a function within another function until C++ 11. At this time the Lambda function, also called an "anonymous" function (a function with no name or declaration in the global scope) was added to try and keep the global scope clean, free of unnecessary functions that are only used once. Strange that something that is so frequently used in JavaScript since forever has been added so late in the game in C++.

The closer we are to C++ in HiseScript, the better we understand our plugins. :)

@d-healey said in (Possible) Breaking change: local variables references inside nested function definitions:

@Christoph-Hart Fast work! I'll play around with this tomorrow and let you know if I hit any issues, but look like a good improvement to me.

Please post any tests you make with lambdas, I would love to have a look at that! :)

(Possible) Breaking change: local variables references inside nested function definitions

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