How does Ada do “narrowing”?
Dave Griffith said . . . Nonetheless, [the Ada 95 designers] chose a structure-based subtyping, with all of the problems that that is known to cause. As the problems of structure based subtyping usually manifest only in large projects maintained by large groups, this is _precisely_ the subtype paradigm that Ada 95 should have avoided. Ada 95’s model is, as Tucker Taft pointed out, quite easy to use for simple OO programming. There is, however, no good reason to _do_ simple OO programming. OO programmings gains click in somewhere around 10,000 LOC, with greatest gains at over 100,000. At these sizes, “just declare it tagged” will result in unmaintainable messes. OO programming in the large rapidly gets difficult with structure based subtyping. Allowing by-value semantics for objects compounds these problems. All of this is known. All of this was, seemingly, ignored by Ada 95. (Tucker Taft answers) As explained in a previous note, Ada 95 supports the ability to hide the implementation he
Dave Griffith said . . . Nonetheless, The Ada9x committee chose a structure-based subtyping, with all of the problems that that is known to cause. As the problems of structure based subtyping usually manifest only in large projects maintained by large groups, this is _precisely_ the subtype paradigm that Ada9x should have avoided. Ada9x’s model is, as Tucker Taft pointed out, quite easy to use for simple OO programming. There is, however, no good reason to _do_ simple OO programming. OO programmings gains click in somewhere around 10,000 LOC, with greatest gains at over 100,000. At these sizes, “just declare it tagged” will result in unmaintainable messes. OO programming in the large rapidly gets difficult with structure based subtyping. Allowing by-value semantics for objects compounds these problems. All of this is known. All of this was, seemingly, ignored by Ada9x. (Tucker Taft answers) As explained in a previous note, Ada 9X supports the ability to hide the implementation heritage
