Pharo method with multiple arguments

Question

I am creating a Pharo Class method that takes 3 arguments. I am using the following code and it gives me the error "Variable or expression expected.."

    MethodName: arg1:argValue1 arg2:argValue2
    ^ self var1: argValue1 var2: self var3: argValue2

What would be the correct method declaration syntax? Later on, I intend on calling this method like below :

    ClassName var1: argValue1 var2: self var3: argValue2

Answer 1

The bit that you have to understand when it comes to naming methods in Smalltalk is that the method can be split into multiple parts, delimited by colons (:), and that the arguments are inserted after each of those colons. Semantically, that makes a lot of sense, and allows you to use good naming practices so that your code reads almost like an English sentence (which is why the language was named Smalltalk).

So for a method that, in Java or a similar "curly bracket language", might look something like this:

registerUser(String emailAddress, String password, boolean isAdmin) {...}

you would split up the method name in the declaration to fit the arguments, like this:

registerUserWithEmail: anEmailAddress password: aPassword isAdmin: aBoolean

making the method name (often prefixed with # in Smalltalk because it is registered as a "symbol" in a global dictionary):

#registerUserWithEmail:password:isAdmin:

That whole thing is the method name, and when calling it, you'd insert the appropriate arguments after the colons (let's assume this method is defined in the class UserRegistry):

UserRegistry
    registerUserWithEmail: '[email protected]'
    password: 'topSecret'
    isAdmin: true

Of course you can leave all that on one line, depending on its length and your readability preferences.

Getting back to your case, you had this:

MethodName: arg1:argValue1 arg2:argValue2

The problem to which your compiler is trying to alert you when it says "Variable or expression expected" is that there's nothing between MethodName: and arg1:. I think you may have assumed that MethodName: wasn't part of the method name but part of the definition.

Some notes:

• by convention, method names use lowerCamelCase
• #methodName:arg1:arg2: wouldn't make a very good method name in Smalltalk, because the name should describe what it does and, when arguments come into play, what arguments are expected; the same goes for #var1:var2:var3:
• if you're going to be calling this method by sending a message to ClassName, then that method needs to be defined on the class side of ClassName, not on the instance side
• think about what you're calling/passing in your example - unless you're doing something complicated with a hierarchy of objects, there may not be much point in sending a message to self with one of the arguments being self as well; ask yourself whether you can simplify something there (hard to be more concrete without knowing what you're trying to do)

Answer 2

What you wrote is correct, but MethodName is extra and then your method would look like this:

arg1: argValue1 arg2: argValue2

  ^ self var1: argValue1 var2: self var3: argValue2

Which is a 2 arg method. You can write 3 arg method in a same way:

arg1: argValue1 arg2: argValue2 arg3: argValue3

  ^ self var1: argValue1 var2: self var3: argValue2

Then what you are doing is calling another 3 arg class method #var1:var2:var3: with arguments: argValue1, self, argValue2 (I hope this is your intension because this looks weird).