[JASS] Return bug

[Mechanical Man]

Can somedy explain me the return bug, what it does, how come it does not show error (Usually programming languages do not allow double return statements), what really executes, how can be exploited and be useful (handlevars!), who discovered it (omg!) and why it works on some situations?

I know that it was the first script on wc3sear.ch.

 

[Diablo-dk]

some of the very usefull stuff allowed because of the return bug is the function H2I. the function simply takes a handle(a unit as an example) and stores it as an integer. without this bug, handlevars would'nt be possible. dunno who discovered it or what happens to it, i just know that it's hell usefull.

 

[Mechanical Man]

But handle is variable type (object, class) in jass?

 

[DeT]

yes it is.
RB allow u to store habdles as integer 4 example in cache and use it like variables...

Compiler looks only at last "return" and if it's write it doesn't show an error, so u can create f-ns like H2I I2H I2U etc...

 

[Captain Griffen]

It returns the 4-byte pointer (which is unique for that handle slot) in integer form.

 

[DeT]

so...u can keep handles in cache

 

[Captain Griffen]

No. You can 'attach' things to a handle slot with it, or store a pointer to a handle slot in integer form.

Handle index usage, unlike handle variables (eg: unit/location types), doesn't keep the reference, so can be accidently transfered. That's why new structs are safer (not to mention faster).

 

[DeT]

hm...that sounds better
but result is the same

 

[Captain Griffen]

Result is the same until you hit a problem. Then you don't understand what's going on, so you can't fix it. Understanding is crucial to more complex stuff and troubleshooting.

 

[Mechanical Man]

What I understood is that handle is like Object in java, where everything is inherited from

 

[wyrmlord]

As far as I know, all data types in JASS are 4 bytes in size (excluding strings obviously). The JASS syntax checker overlooks multiple return statements in a single function, only the last return value has to be of the right type (an integer if the function returns an integer, for example). So my guess is in the H2I function, it only returns the handle, but in integer form. Handle variables just take advantage of Gamecache, and store values under the index that the handle points to (each handle has a unique 'index' or number). So you'd use H2I to convert a handle to integer form, and then use I2S to convert that integer to a string and store a value under that:

call StoreInteger(gamecache, I2S(H2I(<handle>)), "some string", <value>)

 

[Captain Griffen]

Strings are also 4 byte pointers. An index is held of all unique strings used. I believe those are reset upon saving/loading though.