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+---- Thread: Can a function return a custom TYPE? (/showthread.php?tid=2794)
Can a function return a custom TYPE? - 12centuries - 06-12-2024
Hello! Former PDS 7.1 developer here, and I recently stumbled on some of my old source code files while digging through an old hard drive. That led me to qb64 and eventually here!
So I decided to take a stab at completing a little text-based map scroller that I started a few decades ago, and I'm using some of the new conventions available with QB64PE.
It brings me my first question: Can a function return a custom TYPE? If so, how?
Consider the following code:
Code: (Select All)
' Split a "label:value" string in to two parts, stored as a custom TYPE
Type config_item_type
Label As String
Value As String
End Type
Dim config_item As config_item_type
line$ = "title: Main Entrance"
config_item = Split_Header_line(lines$)
' Expecting config_item.Label = "title" and config_item.Value = "Main Entrance"
Function Split_Header_Line (line$)
Dim result As config_item_type
i% = InStr(line$, ":")
If i% Then
result.Label = LCase$(Left$(line$, i%))
result.Value = LTrim$(Mid$(line$, i% + 1))
End If
Split_Header_Line = result
END FUNCTION
I get the following two errors:
Expected = similar user defined type on line 10
and
User defined types in expresssions are invalid on line 21
Is this telling me that I can't use TYPEd variables as return types for functions or am I missing something more obvious?
RE: Can a function return a custom TYPE? - SMcNeill - 06-12-2024
You can't use User Defined Types as the function return itself, but you can use them as a parameter and pass the value back and forth.
An example with your code:
Code: (Select All)
' Split a "label:value" string in to two parts, stored as a custom TYPE
TYPE config_item_type
Label AS STRING
Value AS STRING
END TYPE
DIM config_item AS config_item_type
line$ = "title: Main Entrance"
junk = Split_Header_Line(line$, config_item)
' Expecting config_item.Label = "title" and config_item.Value = "Main Entrance"
PRINT config_item.Label, config_item.Value
Split_2 line$, config_item
PRINT config_item.Label, config_item.Value
FUNCTION Split_Header_Line (line$, result AS config_item_type)
i% = INSTR(line$, ":")
IF i% THEN
result.Label = LCASE$(LEFT$(line$, i%))
result.Value = LTRIM$(MID$(line$, i% + 1))
END IF
END FUNCTION
SUB Split_2 (line$, result AS config_item_type)
i% = INSTR(line$, ":")
IF i% THEN
result.Label = LCASE$(LEFT$(line$, i%))
result.Value = LTRIM$(MID$(line$, i% + 1))
END IF
END SUB
As you can see, you can pass those values via parameter; just not as a return through the function itself. (Which might make it just easier to use a SUB, as I've included above as a demo for you, as well. )
RE: Can a function return a custom TYPE? - mdijkens - 06-13-2024
(06-12-2024, 11:16 PM)SMcNeill Wrote: You can't use User Defined Types as the function return itself, but you can use them as a parameter and pass the value back and forth.I would use the function and return i%
An example with your code:
Code: (Select All)' Split a "label:value" string in to two parts, stored as a custom TYPE
TYPE config_item_type
Label AS STRING
Value AS STRING
END TYPE
DIM config_item AS config_item_type
line$ = "title: Main Entrance"
junk = Split_Header_Line(line$, config_item)
' Expecting config_item.Label = "title" and config_item.Value = "Main Entrance"
PRINT config_item.Label, config_item.Value
Split_2 line$, config_item
PRINT config_item.Label, config_item.Value
FUNCTION Split_Header_Line (line$, result AS config_item_type)
i% = INSTR(line$, ":")
IF i% THEN
result.Label = LCASE$(LEFT$(line$, i%))
result.Value = LTRIM$(MID$(line$, i% + 1))
END IF
END FUNCTION
SUB Split_2 (line$, result AS config_item_type)
i% = INSTR(line$, ":")
IF i% THEN
result.Label = LCASE$(LEFT$(line$, i%))
result.Value = LTRIM$(MID$(line$, i% + 1))
END IF
END SUB
As you can see, you can pass those values via parameter; just not as a return through the function itself. (Which might make it just easier to use a SUB, as I've included above as a demo for you, as well. )
when returned you might want to know if the config_item was changed
RE: Can a function return a custom TYPE? - 12centuries - 06-13-2024
(06-12-2024, 11:16 PM)SMcNeill Wrote: You can't use User Defined Types as the function return itself, but you can use them as a parameter and pass the value back and forth.Ah, I completely forgot about that. It's like passing a parameter by reference in other languages. Thank you!
[...]
As you can see, you can pass those values via parameter; just not as a return through the function itself.
(06-13-2024, 12:54 PM)mdijkens Wrote: I would use the function and return i%That is very good point! I was just going with "IF LEN(config_item.label) THEN" but I like your way better. Thank you!
when returned you might want to know if the config_item was changed