Scala shell. Declare same varibale name multiple times

Question

In Scala Shell, I can declare same variable multiple times and I am not getting any error/warning

For Example

scala> val a = 1
a : Int = 1
scala> val a = 2
a : Int = 2
scala> val a = 1
a : Int = 1
scala> lazy val a = 1
a : Int = <lazy>

Here variable name "a" is declared multiple times with var, val and lazy val

So I would like to know

1. How scala complier took this? eg: val a = 1 and var a = 2 which is higher precedence?
2. Why Scala shell is accepting while declaring the same name of variable multiple time?
3. How do i know whether declared variable is mutable or immutable since the same variable name is declared as var and val?

Note: In IntelliJ, Able to declare same variable with multiple time and I don't see error but while accessing IDE shows error as "Can not resolve varibale" so what is the use the declaring same variable multiple times?

Answer 1

In the repl, there is often experimenting and prototyping taking place, and redefining a val is most often not by mistake, but intentional.

Precedence is taken what you typed finally successful.

scala> val a: Int = 7
a: Int = 7

scala> val a: Int = "foo"
<console>:12: error: type mismatch;
 found   : String("foo")
 required: Int
       val a: Int = "foo"
                    ^

scala> a
res7: Int = 7

If you aren't sure, whether a name is already in use, you may just type the name, like a in my case, and get a feedback. For undeclared values, you get:

scala> b
<console>:13: error: not found: value b
       b
       ^

But if you paste a block of code with the :pas technique, multiple names in conflict won't work and the whole block is discarded.