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Paul King resolved GROOVY-10943. -------------------------------- Fix Version/s: 5.0.0-alpha-1 Resolution: Fixed Proposed PR merged. > Treat multiple underscores as placeholders in multi-assignment statements and > closure/lambda parameters > ------------------------------------------------------------------------------------------------------- > > Key: GROOVY-10943 > URL: https://issues.apache.org/jira/browse/GROOVY-10943 > Project: Groovy > Issue Type: Improvement > Reporter: Paul King > Assignee: Paul King > Priority: Major > Labels: GEP > Fix For: 5.0.0-alpha-1 > > > Recent Java versions make underscore, "_", an illegal variable name. This is > to allow it to be used as a placeholder as per JEP 302: Lambda Leftovers[1]. > This issue is to explore how better to have such a placeholder in Groovy. > This strengthens an informal convention already in use. Instead of writing > this: > {code} > def (coordX, coordY, unusedZ) = coord3D() > {code} > Sometimes it is written as: > {code} > def (coordX, coordY, _) = coord3D() > {code} > Currently, the underscore is a variable and could be used but the convention > is that > it would be ignored. > This convention doesn't scale if more than one result is to be ignored (here > a double underscore is used for the second ignored result): > {code} > def (coordX, coordY, _, __) = coord3DwithColor() > {code} > This idea being that the following should be valid: > {code} > def (coordX, coordY, _, _) = coord3DwithColor() > {code} > Which currently gives an error for the duplicated variable name. > Another example: > {code} > def (x, _, y, _, z) = 1..5 > assert "$x $y $z" == '1 3 5' > {code} > Similarly, the idea is applicable for lambda parameters (as per the example > in the previously mentioned Java JEP): > {code} > BiFunction<Integer, String, String> biss = (i, _) -> String.valueOf(i) > {code} > We could follow Java's lead and make underscore an invalid variable name but > it might be possible to keep uses of that name except where there is more > than one occurrence of the name. In such a circumstance, use of the name > would no longer reference a variable. We need to check the impacts of > shadowing as per discussions in the JEP. > [1] [https://openjdk.org/jeps/302] > -- This message was sent by Atlassian Jira (v8.20.10#820010)