scala - Missing parameter type for expanded function when not assigned to a variable -

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• type inference fails on set made .toset? 3 answers

i noticed strange behavior of scala compiler. code:

seq("?").toset foreach (println(_)) 

produces following error:

error: missing parameter type expanded function ((x$1) => println(x$1))         seq("?").toset foreach (println(_))                                         ^ 

same happens this:

seq("?").toset foreach (x => println(x)) 

i found 2 ways around this. ether specify type explicitly:

seq("?").toset[string] foreach (println(_)) 

or save variable:

val s = seq("?").toset s foreach (println(_)) 

is reasonable behavior or compiler bug? doesn't make lot of sense me. how explained?

it expands to:

seq("?").toset foreach (println(x=>x))