Need for `implicit` keyword on parameters

[Craig Tataryn]

Is there a real need for specifying the `implicit` keyword in front of a parameter?  Couldn't the compiler -- after parameter binding fails to satisfy all values -- then flip to a strategy which finds suitable implicit values for the missing parameters? 

Regards,

Craig

[Dennis Haupt]

so you want to make implicits implicit? too much magic in my opinion

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[Adriaan Moors]

Sure, technically we could do that, but I don't think it would be good language design -- documenting your intent is important. Type inference is great, but you should still provide full type signatures for public members. 

Without the implicit keyword error messages could not be as informative. Did you mean to have these arguments inferred? Did you want eta-expansion? Or should they have been provided explicitly?

The same argument could be made for the abstract keyword: the compiler could simply complain when you instantiate the class instead of when you accidentally define a class that can't be instantiated.

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[Craig Tataryn]

Well if you think about it, we're already doing so for functions. Bury this somewhere in your code:

implicit def toInt(s:String) = s.toInt

Then do this in scope:

val i:Int = "1"

Same level of magic IMHO

Craig

[Naftoli Gugenheim]

Are you proposing to also leave off the keyword in front of the thing that gets used implicitly? Or just when declaring the parameter that will accept it?

[Craig Tataryn]

Just the keyword before parameter. The argument for this keyword placement seems to have to do with being explicit about when we want to make use of implicits. I'm not sure that is necessary though.

Craig

_____________________________
From: Naftoli Gugenheim <nafto...@gmail.com>
Sent: Sunday, May 29, 2016 8:48 PM
Subject: Re: [scala-debate] Need for `implicit` keyword on parameters
To: Dennis Haupt <d.ha...@gmail.com>, Craig Tataryn <cra...@tataryn.net>
Cc: scala-debate <scala-...@googlegroups.com>