Treat implicit by-name arguments as lazy values #1993
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@milessabin: I got this idea from our conversation at Scala.IO. Does it correspond to what you had in mind? |
With the previous rules, the two test cases produce a diverging implicit expansion. We avoid this by creating for every implicit by-name argument of type T a lazy implicit value of the same type. The implicit value is visible for all nested implicit searches of by-name arguments. That way, we tie the knot and obtain a recursive lazy value instead of a diverging expansion.
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Feb 19, 2017
| @@ -537,27 +543,56 @@ trait Implicits { self: Typer => | |||
| else EmptyTree | |||
| } | |||
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| inferImplicit(formal, EmptyTree, pos) match { | |||
| /** The context to be used when resolving a by-name implicit argument. | |||
| * This makes any implicit stored under `DelayedIplicit` visible and | |||
| } | ||
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| /** formalValue: The value type for which an implicit is searched | ||
| * lazyIplicit: An implicit symbol to install for nested by-name resolutions |
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With the previous rules, the two test cases produce a
diverging implicit expansion. We avoid this by creating
for every implicit by-name argument of type T a lazy implicit
value of the same type. The implicit value is visible for all
nested implicit searches of by-name arguments. That way,
we tie the knot and obtain a recursive lazy value instead of
a diverging expansion.