Bitten by the lambda parameter name

Stephen Colebourne scolebourne at
Wed Jul 17 02:47:54 PDT 2013

On 15 July 2013 15:52, Remi Forax <forax at> wrote:
> This snippet not compile,
>    Kind kind = ...
>    partySetMap.computeIfAbsent(kind, kind -> new HashSet<>()).add(party);
> Each time I write more than a hundred lines of codes that use some lambdas,
> I fall into this trap.
> It's very annoying !

Just to note that it is correct that this not compiling. It should be
viewed from the perspective of a code reader, not a code writer.

There is no visible additional scope here, just an expression like any
other. As a reader (without any further knowledge, including knowledge
about lambdas) I'd expect that expression to have no additional scope,
just like the ternary operator has no additional scope.

Note that a different syntax would have affected this:

  partySetMap.computeIfAbsent(kind, #(kind) {new HashSet<>()}).add(party);

In this case, there is something that looks a lot more like an inner
class and a method, in which case I'd expect the method parameter to
have a different scope.

The borderline case is
  partySetMap.computeIfAbsent(kind, (kind) -> new HashSet<>()).add(party);

where there is something that looks vaguely like a method parameter.
But I don't think its enough to convince me that the parameter should
be in a different scope.


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