require explicit result type for implicit conversions?

[scabug]

Martin wrote on the scala-user list, "In general it's a good idea always to write a result type for an implicit method. Maybe the language should require it."

I've been bitten myself a couple times by problems that went away once I added a result type to an implicit so I thought I'd open a ticket on this.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-801?orig=1
Reporter: @SethTisue
Assignee: @mcdirmid

[scabug]

@mcdirmid said:
We should disallow type annotations on implicit defs to prevent vicious implicit recursive applications. Actually, I follow this rule in my own code when possible, its saved me more than a few times.

[scabug]

@dubochet said:
Sean, can you please elaborate on your contribution a little?

[scabug]

@odersky said:
I have implemented a slightly more permissive rule: An implicit conversion without explicit result type is visible only in the text following its own definition. That way, we avoid the cyclic reference errors. I close for now, to see how this works. If we still have issues we migth come back to this.

[scabug]

@odersky said:
Milestone next_bugfix deleted

[scabug]

@paulp said:
See also #2206. Explanatory error message fixed so it will print in r21706.