Groovy collect（）闭包无法大写字符串

Question

I have a list of objects that are not necessarily a string, and I want to return a list of strings that have been capitalized.

Currently, I'm doing this:

// Input : ["foo", "bar"] (not actually strings)
// Expected Output : ["Foo", "Bar"]
// Actual Output : ["foo", "bar"]

// Code: 
list.collect { it.toString().capitalize() }

What might be the problem? If I print out each element as I go trough collect it prints the correct values, but the final list is wrong.

Answer 1

collect doesn't mutate the original list, but returns a new one:

def oringinal = ["foo", "bar"]
def capitalized = original.collect { it.capitalize() }
println(capitalized) // ["Foo", "Bar"]

PS: you can also use the *. spread-dot operator like so:

def capitalized = original*.capitalize()

Answer 2

You suspect that .collect() method mutates input list, but it does not - it creates a copy of the list and does not change anything in the input list.

def list = ["foo", "bar"]

def newList = list.collect { it.toString().capitalize() }

assert list != newList

assert newList == ["Foo", "Bar"]