How to getaway from "out of bounds" intentionally?

ngdangtu · March 21, 2025, 9:17pm

Godot Version

4.4

Question

Here is the error I got caught with:

E 0:00:00:342   background.gd:56 @ get_variant(): Index p_index = 1 is out of bounds (p_instance->size() = 1).
  <C++ Source>  core/variant/variant_call.cpp:681 @ func_Array_get()
  <Stack Trace> background.gd:56 @ get_variant()
                background.gd:46 @ load_bg_part()
                background.gd:31 @ _ready()

So basically I have a piece of data that is an Array of a Dictionary. So I write a function, get_variant(), to ensure it can return a fallback of value in case the index is out of bound. So yes, I expect “out of bound” senario. The inside function look like this:

func get_variant(inx: int, type: String):
	if !variant_map.get(inx): return ''
	if !variant_map[inx].get(type): return ''
	return variant_map[inx][type]

Before that I did this but due to the error I have to try different way (and it’s still no hope)

const variant_value = variant_map[inx][type] if variant_map.get(inx) else ''

Is there anyway to get rid of the error because I want that error happens. It simply a case where I already covered.

Update ===

The closest topic I found is this How to call an out of bounds index on an array without an error. However the method was suggested in the answer was suitable to godot 4.4 anymore as I couldn’t find it in the doc.

tibaverus · March 21, 2025, 9:20pm

I believe there’s a function called has() which you can use instead. This will avoid the exceptions about out of bounds.

ngdangtu · March 21, 2025, 9:22pm

Ok, so that is one good news. However has in the array only for checking value not for index

But thanks for the info, lemme fix the dictionary mistake.

ngdangtu · March 21, 2025, 9:24pm

I had fixed with your note but the problem is still here. I think it is the problem coming from the array that wrap the dictionary rather then the dictionary itself.

tibaverus · March 21, 2025, 9:27pm

I feel like it’s not ideal to write code that fails intentionally. I would suggest writing this function / class in such a way that either avoids failure states, or you handle exceptions before they happen.

Maybe check how large your dictionary is before you try to get something out with an index?

ngdangtu · March 21, 2025, 9:33pm

Sometime you have to do it wrong to get the right result. But thanks for the idea, that seems work.

I just think that missing out a solution to handle the error is such a mistake in gdscript. Also, the same has method but dictionary accept index and array is value? I wouldn’t do that if I was them. And even if the array.has(value) makes sense it still not very flexible in returning value. A returned index int would be more useful than just boolean.

tibaverus · March 21, 2025, 9:36pm

Usually if your code fails, it’s better to understand why it does, and if you feel like there’s no correct fix, then perhaps the way you approached the given problem was incorrect to begin with. It’s worth exploring other ways on how to solve a given task / problem.

ngdangtu · March 21, 2025, 9:47pm

Nope buddy, this is design, not an accident.

tibaverus · March 21, 2025, 9:52pm

This was already discussed once and the community agrees on it, see:

https://www.reddit.com/r/godot/comments/14tjet7/why_no_trycatch_what_else_to_use/

github.com/godotengine/godot-proposals

Exception handling (try catch) in gdscript

opened 12:54AM - 24 Jun 22 UTC

closed 09:50AM - 24 Jun 22 UTC

Gnumaru

topic:gdscript

### Describe the project you are working on A 2d platformer ### Describe t…he problem or limitation you are having in your project none ### Describe the feature / enhancement and how it helps to overcome the problem or limitation The title is a clickbait. I DO NOT propose adding try-catch to gdscript. I would merely like to discuss alternatives. It has already been stated that try-catch will never come into gdscript. I'm perfectly fine with that. https://github.com/godotengine/godot/issues/3516 However, I would like to discuss with other users if there is another way of making life easier for those that need to deal with a lot of error handling. This "making life easier" could or could not involve changes to gdscript. Currently gdscript encourages usage of int error codes for error handling. So, a user that has a series of function calls that need to be checked can make it this way: ```gdscript # EXAMPLE 1 var error_code:int error_code = func1() if error_code: return error_code error_code = func2() if error_code: return error_code error_code = func3() if error_code: return error_code ``` The ifs can become single liners ```gdscript # EXAMPLE 2 var error_code:int error_code = func1() if error_code: return error_code error_code = func2() if error_code: return error_code error_code = func3() if error_code: return error_code ``` And let's not forget that gdscript supports semicolons ```gdscript # EXAMPLE 3 var error_code:int error_code = func1(); if error_code: return error_code error_code = func2(); if error_code: return error_code error_code = func3(); if error_code: return error_code ``` If I'm not mistaken, that's the limit with current gdscript. Try-catch will never come. That's okay. If it did come, it could be like this ```gdscript # EXAMPLE 4 try: func1() func2() func3() except err: return err ``` But it will never come, and that's totally fine. So, what can be done to make the user experience more pleasant, similar to a try-catch? Perl 5 has an interesting concept called "default variable". It is a local variable that is already declared in any context. Functions with apparently discarded return values instead have the return values assigned to the default variable. And single parameter functions called without the parameter actually use the default variable as argument. If gdscript had a perl like default variable named _ (underscore), or any other name, like _default, we could rewrite example 3 like this: ```gdscript # EXAMPLE 5 func1(); if: return func2(); if: return func3(); if: return ``` The if without an expression uses the default variable, and the return without value uses the default variable also. But whe could go further and create a new language construct, a pseudo-function called catch(), that would be replaced by the parser with "if _default: return _default". If this pseudo-function existed, we could rewrite example 5 like this ```gdscript # EXAMPLE 6 func1(); catch() func2(); catch() func3(); catch() ``` or like this ```gdscript # EXAMPLE 7 func1() catch() func2() catch() func3() catch() ``` or maybe catch() could receive the function call as argument, so example 6 could be rewritten like this: ```gdscript # EXAMPLE 8 catch(func1()) catch(func2()) catch(func3()) ``` since the function return values are being stored in the default variable, the value can be reused in a chain of function calls ```gdscript # EXAMPLE 9 catch(func1()) catch(func2(_default)) # here _default contains the return value of func1() catch(func3(_default)) # here _default contains the return value of func2() ``` But since in perl a missing function parameter uses the default variable, writing the _default as parameter for func2() and func3() would be optional. I know that a real exception handling system would be complex, since an exception could be thrown anywhere in a code block, like in a nested function call ```gdscript # EXAMPLE 10 func1(func2(func3(func4()))) ``` But leveraging code replacement, we could implement a poor man's try-catch using the parser alone, with the limitation that it would only "catch" exceptions in "root" statements, not in nested ones. So, a poor man's try-catch would be written like this ```gdscript # EXAMPLE 11 try: func1() func2() func3() ``` and would be transpiled to the manual error handling scheme ```gdscript # EXAMPLE 12 var error_code:int error_code = func1() if error_code: return error_code error_code = func2() if error_code: return error_code error_code = func3() if error_code: return error_code ``` Without a catch block, without finally, just a try without catch. ### Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams already described above ### If this enhancement will not be used often, can it be worked around with a few lines of script? already described above ### Is there a reason why this should be core and not an add-on in the asset library? already described above

ngdangtu · March 21, 2025, 9:56pm

Try rust error handling: Error Handling - The Rust Programming Language

system · April 20, 2025, 9:56pm

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