[jdt-core-dev] extended operands in infix expressions - compiler AST out

["Olivier Thomann" <Olivier_Thomann@xxxxxxx>]

Question from Rory Lucyshyn-Wright:

I have a question regarding whether or not I can expect an AST returned by
the AST.parseCompilationUnit(...) methods to have certain properties.

Let T be an AST, representing a compilation unit, as returned by a
parseCompilationUnit(...).
Let the compilation unit's source code contain an expression E:

<Exp1> op <Exp2> op ... op <ExpN>

where the N is an integer greater than or equal to 2, op is a binary
operator, and the <Expi> are expressions at higher precedence than E.
Let S be the subtree of T representing E.

(note:  I have included cases where E is <Exp1> op <Exp2>)
(note:  The root of S will be an InfixExpression whose operator is op)

My question:
Is the following statement true?
No (direct) child of the root of S will be an InfixExpression whose
operator is op.


Discussion:

What I am asking is whether or not expressions like the following will
always be represented as one single InfixExpression whose extended operands
include all but the first 2 terms (or whether they will sometimes involve
more '+' InfixExpression nodes):

1 + 2 + 3 + 4 + 3
or
a*b + 2 + foo()

I am basically asking whether the InfixExpressions will always contain as
many nodes as possible in their extendedOperands lists.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Answer: The extentedOperands list is only used if ALL operators of an
expression are identical.
Therefore 1 + 2 + 3 + 4 + 3 will be represented by an infixexpression build
like this:
LeftOperand: NumberLiteral  1
RightOperand: NumberLiteral 2
extendedOperands: NumberLiteral 3, NumberLiteral 4, NumberLiteral 3
Operator: PLUS

Whereas a*b + 2 + foo() will be represented by an infixexpression build
like this:
LeftOperand:
      InfixExpression
            LeftOperand:
                  InfixExpression
                        LeftOperand: SimpleName a
                        RightOperand: SimpleName b
                        extendedOperands: empty
                        Operator: TIMES
            RightOperand: NumberLiteral 2
            extendedOperands: empty
            Operator: PLUS
RightOperand: MethodInvocation foo()
extendedOperands: empty
Operator: PLUS

Hopefully this clarifies the infix expression.

Olivier