Can't assign to method arguments?

Question

I designed a UI for sending basic email which can be done through

    SMTPClient  
    deliverMailFrom: sender
to: recipients
text: message
usingServer: '' .

I have a method that will take Email ,subject all headers from user. Here is my Method.

 AddHeader:Headername Email: asString Message:message --> "I want to update this"

 " update is nothing but adding dictionay values to that "
|data|
 data:= Dictionary new.
 'To'= Headername ifTrue[data at:#To put:Email.].
 'From'= Headername ifTrue[data at: #From put:Email].
 'subject'= Headername ifTrue[data at: #subject put:Email].

"adding dicitonay values to message"
message:= String streamContents:[:stream|
data values do:[:each| stream nextPutAll: each ]
    separatedBy: [ stream nextPut: Character space ]].

When i try to save this method i get an error saying Cannot store into message. so whats the right way to add values into message that's already been defined.

And other thing values added from dictionary are not added in the order they been put. so is there a way i can add these values in order they been put like To first, From next , then subject..

It's a compiler error to store into a method parameter. Often one will create a temporary variable to do manipulations. — ShyPerson, Feb 06 '13 at 19:32

Andrés Fortier · Accepted Answer · 2013-01-29T11:18:01.703

I don't know if you are asking just for the error or if you are trying to achieve something else on top of what your code does. Since the code is scattered and incomplete I can't give you a proper answer, but I'll adapted a code similar to yours and it seems to work:

|data|
data:= Dictionary new.
('To'= 'To') ifTrue: [data at:#To put:'someone@mail.com'].
('To'= 'Another thing') ifTrue: [data at:#To put:'shouldnt appear'].
data at:#From put:'me@mail.com'.

message:= String streamContents:
            [:stream|
                    data values 
                            do:[:each| stream nextPutAll: each ]
                            separatedBy: [ stream nextPut: Character space ]].

If you copy this in a workspace and inspect the data contents it will give you the following ByteString 'someone@mail.com me@mail.com'. But I think that you have already accomplished this task. Could you elaborate a bit more on what you are looking for and put the complete code, just as you coded it?

Edit based on the OP clarification

Ok, now I see the problem. The thing is that in Smalltalk you don't have "out" parameters and that is why the compiler is telling you that it can't store new contents in the message parameter. From the point of view of the object sending the message, you see that message send as telling an object to perform an action and passing the required collaborators to that object to perform it. If there is a response from the message send it is expected to be in the return value. I re-wrote your method a little bit here to do that:

addHeader: headerName email: aString message: aMessage 

| data newValues |

 data:= Dictionary new.
 'To'= headerName ifTrue: [data at:#To put: aString.].
 'From'= headerName ifTrue: [data at: #From put: aString].
 'subject'= headerName ifTrue: [data at: #subject put: aString].

"adding dicitonay values to message"
newValues := String streamContents:[:stream|
data values do:[:each| stream nextPutAll: each ]
    separatedBy: [ stream nextPut: Character space ]].
^aMessage  , newValues.

as you can see the idea is to use the #, message to join the two strings and return the new value. Some things to note here are:

I changed a little bit the names to use a more accepted capitalization pattern.
You may want to take a look at the #asSymbol message to avoid the if statements.

HTH

Thanks i didn't know i could concatenate . – Irfan Jan 30 '13 at 04:51 — Irfan, Jan 30 '13 at 04:51

Can't assign to method arguments?

1 Answers1