CODEWITHSUNDEEP
flutterdart
Drew Bartlett
Drew Bartlett

Reputation: 1901

How deep do you need to nest const constructors in dart?

I've been trying to leverage const constructors more in my Flutter app lately and I'm curious how deep I need to include the const keyword. Take the following:

const Text('foo', style: const TextStyle(fontSize: 12));

I know I can make the Text widget a const because it's a static string. I can also make the TextStyle a const. But do I need to even include const on the TextStyle if its parent Text is also a const?

Additionally, if it is the case that I do not need to put a const inside a const and change it to the example below, will the second TextStyle be the same instance as the first?

const Text('foo', style: TextStyle(fontSize: 12));


/// is this TextStyle the same instance as above?
Text(foo.bar, style: const TextStyle(fontSize: 12));

I'd really appreciate any input on this. I struggle to know if I should be littering the codebase with const or if it's a waste of my time. Thanks in advance!

Upvotes: 1

Views: 154

Answers (2)

jamesdlin
jamesdlin

Reputation: 90155

const specifies that an object can be initialized at build time. Therefore, const T(x) requires that x be known at build time, which means that it also must be const. Therefore, for const T(U()), adding a const qualifier when constructing U is unnecessary; it's inferred from the context.

If U is not const-constructible, then you'll get a build-time error.

Upvotes: 3

Thierry
Thierry

Reputation: 8393

There is no need to do littering the codebase with const.

These are equivalent:

BAD

final b = const [const A()];

GOOD

final b = const [A()];

If you use Lint in your project, the following rule will be useful to detect unnecessary const keywords: unnecessary_const

Don't struggle with these, let Lint tell you what to do.

Upvotes: 4

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