Why not set the value directly

Question

I'm reading the source of a project, and found such code there:

private var _responded: Boolean = _ { _responded = false }

I don't understand why he wrote it like this, isn't it the same as:

private var _responded = false

What's the difference between them?

That's puzzling. I'm wondering if it has something to do with the linearization of multiple inherited traits. — Kipton Barros
– Kipton Barros, Commented Aug 17, 2011 at 4:52
No difference that I know of. Perhaps it would be a good idea to ask the author? — Alexey Romanov
– Alexey Romanov, Commented Aug 17, 2011 at 5:03
Re: multiple inheritence -- scratch that, vars can't be overridden. — Kipton Barros
– Kipton Barros, Commented Aug 17, 2011 at 5:08

Ngoc Dao · Accepted Answer · 2011-08-17 14:14:47Z

I'm the author of that code.

Writing like this:

private var _responded = false

causes this warning on compilation (with older versions of Scala, seems no problem with Scala 2.9):

the initialization is no longer be executed before the superclass is called

You can google about that warning to find more information.

Kevin Wright · Accepted Answer · 2011-08-17 08:30:55Z

6

I'm going to hazard a guess here, but that looks a lot like the code produced by intellij's automatic Java to Scala conversion.

This converter tries to maintain the semantics of the original Java as closely as possible, and so tends to produce very non-idiomatic code, as well as lots of nested scopes and mutable variables.

answered Aug 17, 2011 at 8:30

Kevin Wright

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2 Comments

Kipton Barros Over a year ago

Do you know how the semantics differ between the two (var initialized inline, or in a separate block)?

Kevin Wright Over a year ago

For most intents and purposes they're the same. In come scenarios though, there's an (admittedly small) risk of another thread reading the uninitialised value when the declaration and assignment are discrete statements.

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