[#XTENLANG-1173] Does 'for' allow multiple comma-separated variables? - jira.codehaus.org

Details

Type: Bug
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: None
Fix Version/s: None
Component/s: Language Specification
Labels:
None

Number of attachments :
0

Description

If you can have:

for (var i : Int = 1, j : Int = 11; ...)

Then the manual should say so.
(If not, maybe lang improvement?)

Activity

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Igor Peshansky added a comment - 19/Mar/10 9:19 AM

More importantly, can you have multiple for update statements, e.g.,

for (...; ...; i++, j--)

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Igor Peshansky added a comment - 19/Mar/10 9:19 AM More importantly, can you have multiple for update statements, e.g.,

for (...; ...; i++, j--)

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Bard Bloom added a comment - 19/Mar/10 12:27 PM

Committed revision 13468.

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Bard Bloom added a comment - 19/Mar/10 12:27 PM Committed revision 13468.

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Igor Peshansky added a comment - 19/Mar/10 1:44 PM

The following works:

public class XTENLANG_1173 {
  public static def main(Rail[String]) {
    for (var i:Int = 3, j:Int = 8; i < j; i++, j--)
      Console.OUT.println(i+"->"+j);
  }
}

and prints
3->8
4->7
5->6

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Igor Peshansky added a comment - 19/Mar/10 1:44 PM The following works:

public class XTENLANG_1173 {
  public static def main(Rail[String]) {
    for (var i:Int = 3, j:Int = 8; i < j; i++, j--)
      Console.OUT.println(i+"->"+j);
  }
}

and prints 3->8 4->7 5->6

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Bard Bloom added a comment - 19/Mar/10 1:49 PM

But this doesn't:

def fearsome() = {
       

        for(var i : Int = 1, var j : Int = 2; i < 100; i++) {
    	   
       }
       
   }

So it looks like I can have only one statement, but a var statement can have several clauses.

Twelve of one, a half-dozen of the other, but probably worth noting in the manual there.

Thanks.

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Bard Bloom added a comment - 19/Mar/10 1:49 PM But this doesn't:

def fearsome() = {
       

        for(var i : Int = 1, var j : Int = 2; i < 100; i++) {
    	   
       }
       
   }

So it looks like I can have only one statement, but a var statement can have several clauses. Twelve of one, a half-dozen of the other, but probably worth noting in the manual there. Thanks.

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Igor Peshansky added a comment - 19/Mar/10 2:02 PM

Even in C, for loops allow only one variable declaration statement as the initializer (but you can declare multiple variables in that statement).

Syntactically, X10 is more powerful than C here, because in C you can only declare variables of the same type, whereas the only thing they have to share in X10 is their mutability. However, the following fails:

for (var i: Int = 1, j: Double = 10.0; i < 10; i++, j--) {
   Console.OUT.println(i/j);
}

XTENLANG_1173.x10:3: Local variable declarations in a for loop initializer must all be the same type, in this case x10.lang.Int, not x10.lang.Double.
1 error.
Exception in thread "main" polyglot.util.InternalCompilerError: XTENLANG_1173.x10:3,26-41: Local variable declarations in a for loop initializer must all be the same type, in this case x10.lang.Int, not x10.lang.Double.
at polyglot.ast.For_c.typeCheck(For_c.java:133)
at polyglot.ast.JL_c.typeCheck(JL_c.java:180)
at polyglot.visit.TypeChecker.leaveCall(TypeChecker.java:106)
at x10.visit.X10TypeChecker.leaveCall(X10TypeChecker.java:101)

(no reason for it to fail except some misguided notion of C/Java compatibility).

Two variables of different mutability indeed cannot be syntactically declared in the for loop header in X10.

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Igor Peshansky added a comment - 19/Mar/10 2:02 PM Even in C, for loops allow only one variable declaration statement as the initializer (but you can declare multiple variables in that statement). Syntactically, X10 is more powerful than C here, because in C you can only declare variables of the same type, whereas the only thing they have to share in X10 is their mutability. However, the following fails:

for (var i: Int = 1, j: Double = 10.0; i < 10; i++, j--) {
   Console.OUT.println(i/j);
}

XTENLANG_1173.x10:3: Local variable declarations in a for loop initializer must all be the same type, in this case x10.lang.Int, not x10.lang.Double. 1 error. Exception in thread "main" polyglot.util.InternalCompilerError: XTENLANG_1173.x10:3,26-41: Local variable declarations in a for loop initializer must all be the same type, in this case x10.lang.Int, not x10.lang.Double. at polyglot.ast.For_c.typeCheck(For_c.java:133) at polyglot.ast.JL_c.typeCheck(JL_c.java:180) at polyglot.visit.TypeChecker.leaveCall(TypeChecker.java:106) at x10.visit.X10TypeChecker.leaveCall(X10TypeChecker.java:101) (no reason for it to fail except some misguided notion of C/Java compatibility). Two variables of different mutability indeed cannot be syntactically declared in the for loop header in X10.

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Bard Bloom added a comment - 25/Mar/10 12:21 PM

Fixed, rev. 13537

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Bard Bloom added a comment - 25/Mar/10 12:21 PM Fixed, rev. 13537

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Assignee:

Bard Bloom

Reporter:

Bard Bloom

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Dates

Created:

19/Mar/10 8:59 AM

Updated:

25/Mar/10 12:21 PM

Resolved:

25/Mar/10 12:21 PM