how to convert negative int to positive int in flutter

for example if i have a list like

List list = [-12,3,-24,58,12];

i have already tried this ,i did not understand it https://stackoverflow.com/questions/55374813/why-abs-function-in-dart-return-negative-number-when-not-wrapped-in-parenthesi\ i want to convert all parameters to a positive parameters
or if i had only a integer which is negative how to convert it to a positive integer
if you need more information please let me know and thanks for the helps