IntelliJ IDEA offers an easy way to work with type inference feature such as Scala Show Type Info action.

Entering code

  • Let's enter a random code and see what can be done:

    type_info_code

Invoking Show Type Info Action

  • If you select Show type info on mouse hover after, ms check box in Settings | Languages and Frameworks | Scala, then in the Editor, you can simply navigate with the mouse to a value to see its type information.
  • To invoke Show Type Info action in Editor, navigate to the value and press ⌃⇧P or ⌃⇧P⌃⇧P or ⌃⇧P⌃⇧P or ⌃⇧P⌥ Equals, ⌥= or ⌥=⌥ Equals, ⌥= or ⌥=:

    type_info_string

  • You can also see the type information on a value definition. Simply put the caret on a value definition and press ⌃⇧P or ⌃⇧P⌃⇧P or ⌃⇧P⌃⇧P or ⌃⇧P⌥ Equals, ⌥= or ⌥=⌥ Equals, ⌥= or ⌥=:

    type_info_int

Adding Type Annotation

  • To add a type annotation, highlight the value and press ⌘I or ⌘I⌥⏎ or ⌥⏎⌘I or ⌘I⌥ Enter, ⌥⏎ or ⌥⏎⌥ Enter, ⌥⏎ or ⌥⏎:

    type_info_add

    As a result, the type annotation is added:

    type_info_add_result

  • You can also use Adjust types action to shorten types with full qualified names.

    type_adjust

    In this case the necessary imports are added.

    type_adjust_result

Removing Type Annotation

  • You can also remove the type annotation the same way you have added it, by pressing ⌘I or ⌘I⌥⏎ or ⌥⏎⌘I or ⌘I⌥ Enter, ⌥⏎ or ⌥⏎⌥ Enter, ⌥⏎ or ⌥⏎:

    type_info_remove

Seeing Type Annotation on Expression

  • To see the type information on an expression, simply navigate to the expression, highlight it and press ⌃⇧P or ⌃⇧P⌃⇧P or ⌃⇧P⌃⇧P or ⌃⇧P⌥ Equals, ⌥= or ⌥=⌥ Equals, ⌥= or ⌥=:

    type_info_expression