Andrey Hihlovskiy
Professional blog on groovy, gradle, Java, Javascript and other stuff.
Monthly Archives: September 2013
groovy switch: nasty bug
September 20, 2013
Posted by on 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' break default: 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:
switch((int)b)
the program executes “proper” case.
groovy: switch statement and closure comprehension – nice for DSL
September 4, 2013
Posted by on 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 $y" break case isLessThan(y): println "$x is less than $y" break default: println "$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: http://en.wikipedia.org/wiki/Domain-specific_language
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