in delphi7 i have a function that i need to return a array as a result type b
"function createsbox(key:tkey):array[0..255] of byte;" this is not allowed it is expecting a "identifyer expected but array found" is the error throw up. seems to work fine if i declare a record type of array but it seems pointless to do this for one function.
The issue is that you're not allowed to create a new type in a function declaration. But that's what you're doing when you specify the return type as array[0..255] of Byte. Instead, declare a named type, and then use it for the return type:
type
TSBox = array[0..255] of Byte;
function CreateSBox(const Key: TKey): TSBox;
There is a subtle reason for that, and it is in Pascal two array type declarations are not the same "type" regardless of how identical their declaration are, and thereby not assignment compatible. If you write:
var
A: array[1..10] of Integer;
B: array[1..10] of Integer;
A and B are different types. If you write
A := B;
The code won't compile, A and B are different types.
Thereby, if you write
var
A: array[1..10] of Integer;
...
function Foo(...): array[1..10] of Integer;
You're actually declaring a type for the function result - that type would be pretty useless because you could not assign it to A or any array no matter how it s declaration is, for example:
A := Foo(...);
would not work even if the compiler would let you to declare a function that way.
The only way to have a useful function result type thereby is to use a type already declared. Only open arrays are an exception to this rule, but they can be used only as function parameters, not as the result.
okay type TSBox = array of Byte works fine, but using this new type in 2 or more units, could be tricky. 'Cause u will get an error message "incompatible types". There's a partial solution for this situation. U can inform the compiler which unit has that type with this notation: unit.type; Example: Imagine there I have a unit called Web, where I declare the type TDownload. I could do something like this: var fileUrl : Web.TDownload; In this case the compiler will understand that u r using the same type. However, and thats my question for u all: what if u don't want to put that unit in the uses clausule for whatever - circular reference, poo good practices, etc.. What can I do to avoid this problem?
