Re: var vs def

Answering the question, it's "a", the REPL is just printing as usual.

You can google for discussions about recursive variable definitions. You're
correct that it sees the default value on the RHS. That works because
declarations in the REPL are class members, not locals.

You might also consider the scala-user group for questions because it has a
bigger army of helpers.


On Sat, May 2, 2015 at 9:26 AM, scalanewbie <[email protected]> wrote:

> Thank you Martin and Oliver,
>
> This is now clear to me (I think), correct me if am wrong below:
>
> I created another small example, but this time with no variable in var
> declaration. Here is the example, and I start with initialising a variable
> i with 0
>
> scala> var i = 0
>
> i: Int = 0
>
>
> scala> var greatWorld3:Boolean = if (i>10) true else { println("Print
> i:"+i)
>
>      | i += 1
>
>      | greatWorld3 }
>
> Print i:0
>
> greatWorld3: Boolean = false
>
>
> scala> i
>
> res44: Int = 1
>
>
> scala> greatWorld3
>
> res45: Boolean = false
>
>
> Now, I start with a variable i set to 0; and declare a function (I think
> it is still a Function/Method; as when I did not provide *:Boolean*
> return type it complained as being recursive without any return type; do
> correct me if I am getting this wrong).
>
>
> Given that the right side of '=' sign is only evaluated once, the
> statement is run once therefore the i ends up with 1 value at the end of
> it. And for the same reason, the *greatWorld3* variable/function (ummm...
> I am still confused here if I defined a function or variable...) has the
> default for boolean, which is false.
>
>
> And at end of the definition the interpreter prints:
>
>
> greatWorld3: Boolean = false
>
>
> which might have happened either because:
>
>  a. the interpreter returns the type of the just created function/variable
> by default
>
> OR
>
>  b. Because there is a recursive call to greatWorld3, and the interpreter
> prints the vale of greatWorld3.
>
>
> Not sure which one these above 2 is applied?
>
>
> Next I go into function definition, with *def*
>
>
> I then move on to define a new variable j with 0, and now replace the
> definition of greatWorld3 with a function def as below:
>
>
> scala> var j = 0
>
> j: Int = 0
>
>
> scala> def greatWorld3:Boolean = if(j>10) true else {println("Print j:"+j)
>
>      | j += 1
>
>      | greatWorld3 }
>
> greatWorld3: Boolean
>
>
> scala> greatWorld3
>
> Print j:0
>
> Print j:1
>
> Print j:2
>
> Print j:3
>
> Print j:4
>
> Print j:5
>
> Print j:6
>
> Print j:7
>
> Print j:8
>
> Print j:9
>
> Print j:10
>
> res46: Boolean = true
>
>
> scala> j
>
> res47: Int = 11
>
> Output for def block, is all ok.
>
>
> Thanks for your help and time again.
>
>
> Regard,
>
> S
>
>
>
> On Saturday, May 2, 2015 at 2:36:39 PM UTC+1, martin wrote:
>>
>> On Sat, May 2, 2015 at 12:57 PM, scalanewbie <[email protected]>
>> wrote:
>> > Hello All,
>> >
>> > I am a newbie to scala and getting in grasp with val and def.
>> >
>> > I noticed that I could write :
>> >
>> > scala> var greatWorld2 = println("great world")
>> >
>> > great world
>> >
>> > greatWorld2: Unit = ()
>> >
>> >
>> > AND
>> >
>> >
>> > scala> def greatWorld() = println("great world")
>> >
>> > greatWorld: ()Unit
>> >
>> >
>> > Can someone please help me understand the difference?
>> >
>> >
>> > I am aware that var is generally used to define variables and def is
>> used to
>> > define functions.
>> >
>> >
>> > Now, keeping in mind that greatWorld2 is actually a variable and not a
>> > function, I am trying to print it, and I get:
>> >
>> >
>> > scala> greatWorld2
>> >
>> You are probably surprised that you see no output. That's because
>> greatWorld2 returns a unit value (after all, its type is Unit) and the
>> REPL does not print unit values. It could print () but it assumes that
>> you executed the expression for its side effects only.
>>
>> Hope this helps
>>
>>  - Martin
>>
>> >
>> > OR, if I try calling it as a function, it throws an error e.g. below
>> (which
>> > sounds ok as I did not declare this as a function, so was expecting
>> this
>> > anyway).
>> >
>> >
>> > scala> greatWorld2()
>> >
>> > <console>:9: error: Unit does not take parameters
>> >
>> >               greatWorld2()
>> >
>> >
>> >
>> >  Long story short, difference between var and def , in terms of what
>> the
>> > interpreter and or compiler is doing underneath will be very good to
>> > understand.
>> >
>> >
>> > Thanks Guys,
>> >
>> > S
>> >
>> >
>> >
>> > --
>> > You received this message because you are subscribed to the Google
>> Groups
>> > "scala-language" group.
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>>
>>
>>
>> --
>> Martin Odersky
>> EPFL
>>
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