[mcguire]

So you marked the field deprecated and stated it would be removed in release "potato-wedge". The "potato-wedge" release rolls around, you delete the field, and Ted, who didn't care to pay attention to the deprecation warnings, ... does what?

In a statically typed world, Ted tries to compile his project and gets an error saying, "last_name doesn't exist". In a dynamically typed world, Ted ships his code into production (or possibly testing) and gets a call at 4:00a.m. saying it threw an exception or just died. (The testers are in Bangladesh.)

In Alan Kay's world (or at least that of the author), the code goes on robustly producing whatever results it produces in the case where no one has a last name. Better?

[zeugmasyllepsis]

I agree with you! Static typing and more broadly static analysis can help catch some types of backwards incompatibilities. The intent of my comment was to highlight complementary techniques that can minimize the reliance on static analysis as the primary tool for keeping code in sync with dependencies. Alone, any one technique is not particularly fool-proof.