Some tools allow the dist weight operators (:=, :/) to be split instead of a single token.
To keep your code portable, stick to the standard way of writing those operators.
class Fly;
rand int val;
constraint cst_sum {
val dist {1 : = 10, 4 : / 20};
}
endclass
class Fly;
rand int val;
constraint cst_sum {
val dist {1 := 10, 4 :/ 20}:
}
endclass