Andrey Hihlovskiy

Professional blog on groovy, gradle, Java, Javascript and other stuff.

Tag Archives: switch

groovy switch: nasty bug

I found nasty error in Groovy compiler. Consider the following code:

byte b = 1
switch(b) {
  case 0..9:
    println 'it is between 0 and 9'
    println 'it is something else'

It executes ‘default’ part, not the part with 0..9, which is not what a programmer would typically expect.
The reason behind it should be related to type conversion between “byte” and “int” types. With the following workaround:


the program executes “proper” case.


groovy: switch statement and closure comprehension – nice for DSL

It is rather easy to extend groovy switch statement with our own DSL:

def isGreaterThan(a, b) { a > b }

def isGreaterThan(b) {
  return { a -> isGreaterThan(a, b) }

def isLessThan(a, b) { a < b }

def isLessThan(b) {
  return { a -> isLessThan(a, b) }

def x = 5
def y = 6

switch(x) {
  case isGreaterThan(y):
    println "$x is greater than $y"
  case isLessThan(y):
    println "$x is less than $y"
    println "$x equals $y"

The trick here is that single-argument versions of IsGreaterThan, IsLessThan return closures. Switch-statement “understands” closures: it passes it’s argument (x in our case) as a parameter to the closure and expects boolean result being returned from the closure.Same thing can be done via function currying, but it looks not so nice, as with function overload.

By the way, DSL stands for “Domain Specific Language”. See more information here:

Power of switch statement in groovy

Very impressive (and expressive):

def x = 'test'

switch(x) {
  case null:
    println 'null!'
  case ~/(?i)Test/:
    println 'got it!'
    println 'something else'

here second ‘case’ does case-insensitive regex comparison. In general, case may contain any regex, collection, range or class.

Ugly bug in Linux Mint/MATE

Whenever you switch between Firefox and Eclipse (Juno/Kepler) and window-compositing is enabled, Caja crashes. That means: menu and taskbar disappear, all Caja windows are closed. The bug is still not fixed in Linux Mint 15 Olivia. I have to switch to Cinnamon 😦