The signature of a generic comparison function.

A comparison function represents an ordering on a type of objects. A total ordering on a type means that for two values, either they are equal or one is greater than the other (and the latter must then be smaller than the former).

A Comparator function represents such a total ordering by returning

- a negative integer if
`a`

is smaller than`b`

, - zero if
`a`

is equal to`b`

, and - a positive integer if
`a`

is greater than`b`

.

typedef Comparator<T> = int Function(T a, T b);

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https://api.dart.dev/stable/2.5.0/dart-core/Comparator.html