Bo Berglund via fpc-pascal <fpc-pascal@lists.freepascal.org> schrieb am Do., 13. Apr. 2023, 07:49:
> What is the use case for "out" compared to "var" when it seemingly is > doing the > same thing? > Or is it exactly this: > With "out" you get a pristine empty variable which you have to initialize > if > needed (setting its length in this case)? > And you are ensured no stale data will be part of it? > When the compiler finds an "out" parameter in a call it does not need to check whether the variable you pass is has been written to. With a "var" parameter you'll get "variable not initialized" warnings/hints instead. It's the task of the called function then to provide a correct value for the parameter. > > > >And if so, what is the rule for *when* to use var in function call > argument > >> lists for items that will be changed inside the called function and used > >> afterwards > >> > > > >The rule is simple: if you need to modify the parameter value itself (e.g. > >changing a primitive type, changing a field in a record, changing an > >array's length or data, changing the value of a class instance - but not > >its fields!) you need to pass it as "var". > >If it's a write only parameter you can even use "out". > > So "out" it is unless I need to use the existing data or append new data > to it, > in which case I need "var", right? > Correct. Regards, Sven >
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