Eiffel "Gotchas"

22 May 1997

Gotcha #7 - Answer and Explanation

Here's the question again:

How can you break a valid, working program by adding a single pair of parentheses that do not affect the order of computation?

Here's how:

   -- this works:
   a.some_procedure
   b.some_function.some_procedure

   -- this does not compile
   a.some_procedure
   (b.some_function).some_procedure

   -- this works again
   a.some_procedure;
   (b.some_function).some_procedure

The second example fails because the parser ignores line endings, and treats "some_procedure(b.some_function)" as a function call with one argument.

The fix is to separate the instructions with a semicolon, which makes it clear to the parser when we have reached the end of the first instruction.

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Eiffel "Gotchas"