Help understanding how to handle a return value

Don M · 2012-09-09 08:29

If I have a method that will return a value how do I handle the value on the return to the calling method?

For instance:

pub some_method  |  response

  some code
  if this happens
    response := 1
  else
    response := 0

  return response

In the calling method I call some_method but I don't know how to bring in the response. Hope you understand what I'm asking.

Thanks.
Don

Don M · 2012-09-09 08:34

A little more clarification.

My main code might be this:

Pub  Main

  some code
  some_method
  some more code

So after I return from some_method how do I react to the value returned?

StefanL38 · 2012-09-09 08:51

HI Don,

for this yofine a global long
The call for your method is then used as assignemt to this variable see code example below

VAR
  long MyGlobalVarForResponse

PUB Main
  MyGlobalVarForResponse := some_method


if MyGlobalVarForResponse == 0
  Do that
else
  Do this


pub some_method  |  response    some code   if this happens     response := 1   else     response := 0    return response

best regards
Stefan

JonnyMac · 2012-09-09 08:52

Easy-peazy:

someValue := some_method

It's important to remember that a method can only return one long. If you're clever, you can pack it as two words or four bytes. If I need a method to affect multiple values I pass the starting address of those values to the method.

Phil Pilgrim (PhiPi) · 2012-09-09 10:03

Don_M,

In addition to Jon's comments, you can eliminate the return statement by making response the automatic return value. Just place a colon ([noparse]:[/noparse]) in front of its declaration, instead of the vertical bar (|).

pub some_method  :  response

  some code
  if this happens
    response := 1
  else
    response := 0

-Phil

Don M · 2012-09-09 12:47

Thanks guys. I have tried all 3 implementations and now understand.

msrobots · 2012-09-09 13:09

A method in spin is actually a function returning a long value. Allways.

The implicit return-value (if you do not return anything with RETURN) is a variable called RESULT.

So if you not retun anything by yourself (not using RETURN statement) you can imagine a RETURN RESULT at the end of your method even if it is not standing there.

The variable RESULT is allway defined and in OPPOSITE to all local variables you declare after the | it is initialised to 0. ALL OTHER local Variables you declare ARE NOT initialised to anything. This one got me a couple of times until I found out.

So

pub some_method  |  response

  some code
  if this happens
    response := 1
  else
    response := 0

  return response

is the same as

pub some_method  

  some code
  if this happens
    RESULT:= 1
  else
    RESULT:= 0

And if you like to rename the implicit return-value RESULT to somethin else, to make your code more self-documenting you can do this also - as Phil showed using a : after the method-definition and before the |

pub some_method :  response

  some code
  if this happens
    response := 1
  else
    response := 0

StefanL_38 is not right in saying you need a global variable to read the result of a function/method-call, you do not. You can use a local variable or not even a variable at all - since you can use the return-value as is.

so this will work without a global variable

PUB Main | myLocalVarForResponse
  myLocalVarForResponse:= some_method

if myLocalVarForResponse == 0
  Do that
else
  Do this

and this without any variable

PUB Main 
if some_method== 0
  Do that
else
  Do this

I hope this will answer your question.

Enjoy!

Mike

Help understanding how to handle a return value

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