Can a function return a custom TYPE?

[12centuries]

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?

[SMcNeill]

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. )

[mdijkens]

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. )

I would use the function and return i%
when returned you might want to know if the config_item was changed

[12centuries]

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.   
[...]
As you can see, you can pass those values via parameter; just not as a return through the function itself.

Ah, I completely forgot about that. It's like passing a parameter by reference in other languages. Thank you!

I would use the function and return i%
when returned you might want to know if the config_item was changed

That is very good point! I was just going with "IF LEN(config_item.label) THEN" but I like your way better. Thank you!