Why does shared mutable state tangle a program?
One talk separates identity from its successive values. The other shows how state couples parts of a system through time. Read them together to identify what a caller must know about earlier operations.
Read on through a shared source
Can today’s record explain yesterday’s decision? →Keep the value a decision actually used so that later changes do not erase its explanation.What does a snapshot promise its reader? →Stable snapshots let observers read a particular version. Treating information as values explains why that version can be passed on without changing its meaning.Why does testing a business rule need a database? →Separate who qualifies for a reminder from whether the reminder can be delivered.
Compare the passages
key characteristic of a value is that it's immutableHaving state in your program is never simple, right?