[dart-misc] Newbie question about const

[Kovács Attila]

Hi

Could somebody tell me what is the difference between them :


1. const List<String> li = ["a","b"];

vs.

2. List<String> li = const ["a","b"];

vs.

3. const List<String> li = const ["a","b"];

thank you in advance

[Tom M]

Hi Atilla,

1 and 3 are the same. Since the left-hand side is a const declaration, the
right-hand side *must be* a transitively constant value. This const
keyword can be inferred, and Dart style prefers
<https://www.dartlang.org/guides/language/effective-dart/usage#dont-use-const-redundantly>
to omit it.

In 2, the value is assigned to an ordinary mutable variable. Note Dart
constants are canonicalized: each variable points to the same object, so
they are all == and identical.

If you write List<String> li = ['a', 'b'] instead, a constant value is *not*
inferred. A new list is allocated.

https://dartpad.dartlang.org/acb3d4f93aaab8fdd6b03fa7d5e4b2eb

Hope it helps!

PS. You can omit types too. Dart can infer from the assignment that li is a
List<String>.

On Fri, Oct 12, 2018 at 9:49 PM Kovács Attila ***@gmail.com
<http://mailto:***@gmail.com> wrote:

Hi

Post by Kovács Attila
1. const List<String> li = ["a","b"];
vs.
2. List<String> li = const ["a","b"];
vs.
3. const List<String> li = const ["a","b"];
thank you in advance
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[Kovács Attila]

Thank you for your detailed explanation. It was very useful.
Attila

Post by Kovács Attila
Hi
1. const List<String> li = ["a","b"];
vs.
2. List<String> li = const ["a","b"];
vs.
3. const List<String> li = const ["a","b"];
thank you in advance