An intricate look at the Dafny reads and modifies concepts? #1899
-
In reading about
So basically:
So basically, it is for some reason necessary for proving properties of code. Why is it infeasible without them? What infeasible things do these make feasible? What properties are traditionally difficult/impossible to prove, and how does Also, how does this compare to other programming languages/concepts? How does it relate to, for example, Rust's immutable/mutable variable declarations, or the borrowing system? I am having difficulty understanding the need for the Thank you very much for the help. |
Beta Was this translation helpful? Give feedback.
Replies: 1 comment 2 replies
-
Your summary is exactly right. The short and more general answer to your question, applicable to many verification tools, is that it's primarily for efficiency: to make a difficult problem feasible. Due to one of Dafny's key design decisions (also made for efficiency, of both human mental resources and computational resources), it turns out to be necessary in the Dafny case to make verification possible at all. The key reason for this is that Dafny (like many similar tools) verifies each method independently. When analyzing the body of a method, Dafny assumes that the preconditions ( This process interacts with memory in a somewhat complex way. Typically, an executing program has many objects in memory, only a few of which are of interest to any given method. It's important for program modularity that a single method can be called from many contexts, each of which may have different memory contents. The The alternative to this would be to look inside the body of the called method to see what it actually does in the context of the specific caller being analyzed. That would require the verification process to consider much more code at once, and would require each method to be re-analyzed in every place where it gets called, which in practice is typically so expensive as to be infeasible. Rust's type system is another approach at solving a similar problem in a more constrained context. Giving a reference parameter the |
Beta Was this translation helpful? Give feedback.
Your summary is exactly right. The short and more general answer to your question, applicable to many verification tools, is that it's primarily for efficiency: to make a difficult problem feasible. Due to one of Dafny's key design decisions (also made for efficiency, of both human mental resources and computational resources), it turns out to be necessary in the Dafny case to make verification possible at all.
The key reason for this is that Dafny (like many similar tools) verifies each method independently. When analyzing the body of a method, Dafny assumes that the preconditions (
requires
clauses) hold before execution and tries to prove that the postconditions (ensures
clauses) will t…