4 ms·

Why underscores in "__data"? Is this just a temporary thing?

MBCook 9y ago
I agree, I hope that doesn’t end up being final. Otherwise I really like this proposal. I absolutely love the ability to do D structuring, and I like the idea that they’re going to make it possible to make these immutable as well.
avemg 9y ago
Probably to avoid making 'data' a reserved word and breaking a ton of code that used 'data' as a variable name. Prior to Java 5, 'enum' was a very popular variable name too.
- aisofteng 9y ago
  I'm having a difficult time trying to think of a case where "data" is the best variable name for anything.
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  - nikolay 9y ago
    Plus, it's 2017! There are so many tools to do a semantic search and replace and replace all variables, parameters, etc. called "data" with, let's say, "__data__". Why uglify the language instead of providing a migration tool like Python's 2to3?!
freeone3000 9y ago
Java reserved words are reserved in all contexts. You can't have a variable called "class" because class is a reserved word. If 'data' becomes a reserved word, imagine the code that would no longer compile...
- cakeface 9y ago
  Not exactly true, but true for this use case. The new module keyword in Java 9 is only a keyword in module-info.java. You can still have a variable named module in regular class files. They wouldn't be able to pull this syntax trick with data as a keyword though.
  - dtech 9y ago
    Why not? `data class X` is currently invalid code. What is the problem with allow the `data` keyword in a class definition and not forbidding it in other contexts?
    - chrisseaton 9y ago
      That's just not the rest of the Java grammar is designed. It would be an unwelcome edge case.
    - cakeface 9y ago
      My first thought is that maybe there is an issue with inner class definitions here. Not sure how you'd define an inner data class but I'm guessing it would be similar to regular classes. If I have a `public class data` already in my codebase and then I have places where I declare a `data variable1` I think that there is potential for issues. I don't have much experience with grammars but I feel like the more contextual the parsing rule the more likely there will be nasty edge cases.
      - dtech 9y ago
        I have experience with grammars, but not with the Java one. There isn't an inherent restriction on context-free grammars why this couldn't happen. In pseudocode this could work fine: classDef = accessModifier? classModifier* `class` identifier `{` (fieldDef|methodDef|classDef)* `}` fieldDef = accessModifier? fieldModifier* type identifier `=` expression classModifier = `data` fieldModifier = `synchronized` | `final` | `volatile` As you can see there isn't an inherent reason why the identifier rule should exclude the `data` keyword for this to work
evacchi 9y ago
It's decoy to avoid bikeshedding. The value class proposal used __value
- nikolay 9y ago
  I hope so!
- billrobertson42 9y ago
  When you say decoy, do you mean it's intentionally gross to keep people from going off on syntax debates?

I agree, I hope that doesn’t end up being final. Otherwise I really like this proposal. I absolutely love the ability to do D structuring, and I like the idea that they’re going to make it possible to make these immutable as well.

avemg 9y ago

Probably to avoid making 'data' a reserved word and breaking a ton of code that used 'data' as a variable name. Prior to Java 5, 'enum' was a very popular variable name too.

aisofteng 9y ago
I'm having a difficult time trying to think of a case where "data" is the best variable name for anything.
- deleted 9y ago
  [deleted]
- deleted 9y ago
  [deleted]
- nikolay 9y ago
  Plus, it's 2017! There are so many tools to do a semantic search and replace and replace all variables, parameters, etc. called "data" with, let's say, "__data__". Why uglify the language instead of providing a migration tool like Python's 2to3?!

freeone3000 9y ago

Java reserved words are reserved in all contexts. You can't have a variable called "class" because class is a reserved word. If 'data' becomes a reserved word, imagine the code that would no longer compile...

cakeface 9y ago
Not exactly true, but true for this use case. The new module keyword in Java 9 is only a keyword in module-info.java. You can still have a variable named module in regular class files. They wouldn't be able to pull this syntax trick with data as a keyword though.
- dtech 9y ago
  Why not? `data class X` is currently invalid code. What is the problem with allow the `data` keyword in a class definition and not forbidding it in other contexts?
  - chrisseaton 9y ago
    That's just not the rest of the Java grammar is designed. It would be an unwelcome edge case.
  - cakeface 9y ago
    My first thought is that maybe there is an issue with inner class definitions here. Not sure how you'd define an inner data class but I'm guessing it would be similar to regular classes. If I have a `public class data` already in my codebase and then I have places where I declare a `data variable1` I think that there is potential for issues. I don't have much experience with grammars but I feel like the more contextual the parsing rule the more likely there will be nasty edge cases.
    - dtech 9y ago
      I have experience with grammars, but not with the Java one. There isn't an inherent restriction on context-free grammars why this couldn't happen. In pseudocode this could work fine: classDef = accessModifier? classModifier* `class` identifier `{` (fieldDef|methodDef|classDef)* `}` fieldDef = accessModifier? fieldModifier* type identifier `=` expression classModifier = `data` fieldModifier = `synchronized` | `final` | `volatile` As you can see there isn't an inherent reason why the identifier rule should exclude the `data` keyword for this to work

evacchi 9y ago

It's decoy to avoid bikeshedding. The value class proposal used __value

nikolay 9y ago
I hope so!
billrobertson42 9y ago
When you say decoy, do you mean it's intentionally gross to keep people from going off on syntax debates?