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leibnitz27 | 6 years ago

Nope - the if condition is not considered in flow analysis. Read the end:

https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.htm...

"14.21. Unreachable Statements It is a compile-time error if a statement cannot be executed because it is unreachable.

This section is devoted to a precise explanation of the word "reachable." The idea is that there must be some possible execution path from the beginning of the constructor, method, instance initializer, or static initializer that contains the statement to the statement itself. The analysis takes into account the structure of statements. Except for the special treatment of while, do, and for statements whose condition expression has the constant value true, the values of expressions are not taken into account in the flow analysis."

discuss

order

vbezhenar|6 years ago

I still don't understand why reachable or unreachable changes the binding from names to local variable/field. The process of identifier resolution should happen before reachability analysis.

Is there some bug or mail list thread with reaction from Java developers?

leibnitz27|6 years ago

I haven't raised mine, as I consider it to be a refinement of the bug noted in https://twitter.com/tagir_valeev/status/1210431331332689920 (Don't know if java devs have responsed to that.)

(again, reachability analysis of unrelated code changes semantics.)

The problem is that this IS defined behaviour - the scope of the instanceof-assigned variable is dependent on whether or not the taken if-statement is provably exiting.

This is intended to allow

  {
    if (!(obj instanceof String s)) return;

    // s exists now.
  }
But it's not been thought through.