How to use a variable for the key part of a map

Use this:

def map = [(A):1, (X):2]

For the value-part it's even easier, since there is no automagic "convert text to string" happening:

def map = [keyA:A, keyX:X]

Further to Joachim's answer, if you want to add entries to an existing map and the keys are variables, use:

def map = [:]
def A = 'abc'
map[A] = 2

If you use:

map.A = 2

It is assumed that you want to use the literal string 'A' as the key (even though there is a variable named A in scope.

Update

As @tim_yates pointed out in a comment, a key variable will also be resolved if you use:

map."$A" = 2

though personally I prefer to use the [A] syntax because refactoring tools might miss the "$A" reference if the variable is renamed