Both the Collection for-in and map() can return some manipulation of elements from a previous collection. Is there ever any reason to prefer using one over the other?

var myList = [1,2,3];
var alteredList1 = [for(int i in myList) i   2]; //[3,4,5]
var alteredList2 = myList.map((e) => e   2).toList(); //[3,4,5]

CodePudding user response：

Use whichever is easier and more readable. That's a deliberately vague answer, because it depends on what you are doing.

Any time you have something ending in .toList() I'd at least consider making it into a list literal. If the body of the map or where is simple, you can usually rewrite it directly to a list literal using for/in (plus if for where). And then, sometimes it gets complicated, you need to use the same variable twice, or the map computation uses a while loop, or something else doesn't just fit into the list literal syntax.

Then you can either keep the helper function and do [for (var e in something) helperFunction(e)] or just do something.map((e) { body of helper function }).toList(). In many cases the latter is then more readable.

So, consider using a list literal if your iterable code ends in toList, but if the literal gets too convoluted, don't feel bad about using the .map(...).toList() approach.

Readability is all that really matters.

CodePudding user response：

Not an expert but personally I prefer the first method. Some reasons:

1. You can include other elements (independent from the for loop) in the same list:

var a = [1, 2, 3];
bool include5 = true;
var b = [
  1,
  for (var i in a) i   1,
  if (include5) 5,
];
print(b); // [1, 2, 3, 4, 5]

2. Sometimes when mapping models to a list of Widgets the .map().toList() method will produce a List<dynamic>, implicit casting won't work. When you come across such an error just avoid the second method.