One function name, two return types?

[Andrew Morton]

Is it possible to have two function declarations which take the same
parameters but return different types depending on how the function is used?

function f(x) as string
' return a string
end function

function f(x) as string()
' return an array of strings
end function

' somewhere in a subroutine:

Dim S As String=f(1) ' calls the string version of f(x)

Dim A As String()=f(2) ' calls the array version of f(x)

Why? Because I'm extracting IPTC metadata from a file, and some metadata has
a single value (e.g. the caption) and some may have multiple values (e.g.
the keywords). I just think it would look neater to have one function name.

Andrew

[Robin Tucker]

Hi Andrew,

Your function can return "Object" and then leave working out which type was
returned up to the caller. A more involved solution would be to construct
an abstract interface or base class and create two classes that implement
it. Your function "f()" can then behave like a factory, taking X's and
returning instances of your interface. However, in essence this is what the
"Object" return is doing, apart from you need to cast it to Array or String
depending on the TypeOf check.

Dim o As Object = f ( p )

If TypeOf (o) Is .....

ElseIf TypeOf (o) Is

Else
Throw New InvalidOperatio nException ( "f returned an invalid type" )
End If


function f (x) As Object

If ( ... ) Then
' return a string
ElseIf ( ... )
' return an array of strings
Else
Return Nothing
End If

End Sub


Robin

"Andrew Morton" <ak*@in-press.co.uk.inv alidwrote in message
news:%2******** ********@TK2MSF TNGP05.phx.gbl. ..

Is it possible to have two function declarations which take the same
parameters but return different types depending on how the function is
used?

function f(x) as string
' return a string
end function

function f(x) as string()
' return an array of strings
end function

' somewhere in a subroutine:

Dim S As String=f(1) ' calls the string version of f(x)

Dim A As String()=f(2) ' calls the array version of f(x)

Why? Because I'm extracting IPTC metadata from a file, and some metadata
has a single value (e.g. the caption) and some may have multiple values
(e.g. the keywords). I just think it would look neater to have one
function name.

Andrew

[Andrew Morton]

Robin Tucker wrote:

Hi Andrew,

Your function can return "Object" and then leave working out which
type was returned up to the caller.

That just sounds... wrong. I'll go with two function names then.

Thanks,

Andrew

[=?ISO-8859-1?Q?G=F6ran_Andersson?=]

Andrew Morton wrote:

Is it possible to have two function declarations which take the same
parameters but return different types depending on how the function is used?

function f(x) as string
' return a string
end function

function f(x) as string()
' return an array of strings
end function

' somewhere in a subroutine:

Dim S As String=f(1) ' calls the string version of f(x)

Dim A As String()=f(2) ' calls the array version of f(x)

Why? Because I'm extracting IPTC metadata from a file, and some metadata has
a single value (e.g. the caption) and some may have multiple values (e.g.
the keywords). I just think it would look neater to have one function name.

Andrew

The return type is not part of the method signature, so you can not have
overloads of a method that take the same parameters and return different
data types.

As Robin suggested, you can return the data as Object, but then you have
to type cast the value after every call.

I would suggest that you just choose different names for the methods.
It's easier to read the code if it's clear from the method name what
kind of data the method returns, so that you don't have to examine the
data that you send into the method to find out what it returns. Even if
the method names becomes a bit longer, the code is still more readable
than if you have to put a type cast around every call to the methods.

--
Göran Andersson
_____
http://www.guffa.com

[Robin Tucker]

Yes, that is the cleaner solution. Particularly from a maintenance
perspective. If the number of functions you need starts to multiply too
much, you can start to think about alternative patterns.
Robin

"Andrew Morton" <ak*@in-press.co.uk.inv alidwrote in message
news:Or******** ******@TK2MSFTN GP06.phx.gbl...

Robin Tucker wrote:

>Hi Andrew,

Your function can return "Object" and then leave working out which
type was returned up to the caller.

That just sounds... wrong. I'll go with two function names then.

Thanks,

Andrew

[Andrew Morton]

Göran Andersson wrote:

Andrew Morton wrote:

>Is it possible to have two function declarations which take the same
parameters but return different types depending on how the function
is used?

I would suggest that you just choose different names for the methods.
It's easier to read the code if it's clear from the method name what
kind of data the method returns, so that you don't have to examine the
data that you send into the method to find out what it returns. Even
if the method names becomes a bit longer, the code is still more
readable than if you have to put a type cast around every call to the
methods.

That's what I'm doing now, unfnortuantly longer names and my typoing
ability... :-)

Thanks,

Andrew

[zacks]

On May 10, 6:23 am, "Andrew Morton" <[e-mail] alid>
wrote:

Göran Andersson wrote:

Andrew Morton wrote:

Is it possible to have two function declarations which take the same
parameters but return different types depending on how the function
is used?

I would suggest that you just choose different names for the methods.
It's easier to read the code if it's clear from the method name what
kind of data the method returns, so that you don't have to examine the
data that you send into the method to find out what it returns. Even
if the method names becomes a bit longer, the code is still more
readable than if you have to put a type cast around every call to the
methods.

That's what I'm doing now, unfnortuantly longer names and my typoing
ability... :-)

Thanks,

Andrew

Why not create a class with three properties as the function type? One
property could serve as an indicator as to which of the other two
properties contains the return value.

[Andrew Morton]

za***@construct ion-imaging.com wrote:

On May 10, 6:23 am, Andrew wrote:

>>Andrew Morton wrote:
Is it possible to have two function declarations which take the
same parameters but return different types depending on how the
function is used?

Why not create a class with three properties as the function type? One
property could serve as an indicator as to which of the other two
properties contains the return value.

I think that's overcomplicatin g it - perhaps even more than returning an
object as suggested previously.

/I/ know what the type of the return value will be, and if the syntax was
there the compiler would be able to deduce which version of the function to
call, in a similar way to being able to overload a function with different
numbers of parameters. But it isn't, so two function names will have to do.

Andrew

[=?ISO-8859-1?Q?G=F6ran_Andersson?=]

Andrew Morton wrote:

That's what I'm doing now, unfnortuantly longer names and my typoing
ability... :-)

With intellisense you rarely have to type the entire names, so I don't
really see long method names as a problem.

Besides, if you really think that the typing is the hardest part of
programming, you can't be writing any challenging code... ;)

--
Göran Andersson
_____
http://www.guffa.com

[Andrew Morton]

Göran Andersson wrote:

Andrew Morton wrote:

>That's what I'm doing now, unfnortuantly longer names and my typoing
ability... :-)

With intellisense you rarely have to type the entire names, so I don't
really see long method names as a problem.

I only found ctrl+space a few days ago <embarrased emoticon>.

Besides, if you really think that the typing is the hardest part of
programming, you can't be writing any challenging code... ;)

The code isn't challenging; the noisy programming environment is :-( -- I am
the whole IT department, so I'm frequently interrupted with "Andrew, can you
show me how to...", "Andrew, we just need this tweaked on the web site...",
etc. And we now have a construction site just the other side of the road
from my desk. Oh how I love jobs that don't need any concentration, like
installing printers or new computers :-)

Andrew