[HN Gopher] A Dumb Introduction to Z3 (2025)
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A Dumb Introduction to Z3 (2025)
Author : y1n0
Score : 62 points
Date : 2026-04-14 02:45 UTC (4 days ago)
(HTM) web link (ar-ms.me)
(TXT) w3m dump (ar-ms.me)
| amelius wrote:
| If the tutorial uses Rust, why didn't they use a solver written
| in Rust? Z3 was written in C++.
| suddenlybananas wrote:
| What solver would you have them use? Z3 is very mature and the
| Rust bindings are pretty good in my (limited) experience.
| amelius wrote:
| I would write the tutorial in C++, for a more direct
| experience.
| volemo wrote:
| I personally like to avoid the "writing in C++" experience.
| :/
| amelius wrote:
| The authors of a powerful solver package thought
| differently.
| onair4you wrote:
| It might have more to do with the first release of Z3
| being in 2012, with the first stable Rust release being
| in 2015. Rather than the authors of Z3 passing some kind
| of judgment on Rust...
| amelius wrote:
| Z3 uses a sophisticated and fast garbage collection
| scheme internally that doesn't mesh well with Rust
| idioms.
| invl wrote:
| It's reference-counted at the boundaries. See https://git
| hub.com/Z3Prover/z3/blob/daf2506b6002149d531cb6c9...
| mcphage wrote:
| The authors of a powerful solver package were solving a
| different problem than the users of a powerful solver
| package, and so different tools may be appropriate.
| suddenlybananas wrote:
| The author might not know C++ and you don't need to use C++
| to effectively use z3.
| Arainach wrote:
| There's nothing "more direct" - the different APIs for
| different languages call into the same underlying library,
| and most of them are more accessible and easier to work
| with than C++.
|
| Z3 is presumably written in C++ for performance, but
| without data I am very confident the vast majority of
| programs that use Z3 consume it via one of the other APIs.
| invl wrote:
| I'm not sure I understand your argument. Z3's API is
| canonically C. There's a C++ wrapper that works pretty well. I
| don't have experience with the Rust wrapper, but I'd imagine
| that works pretty well too.
| wren6991 wrote:
| Z3 struggles with larger problems. CVC5 or Bitwuzla do a lot
| better once you get into anything complex.
|
| If you're familiar with the Z3 Python API, you'll find the CVC5
| one familiar.
|
| Caveat: I mostly do logic design, maybe there are some software
| verification tasks where Z3 comes out ahead. I've never seen one
| though.
| neel_k wrote:
| I do software verification. In my experience, Z3 is
| consistently but noticeably better than CVC5 at the kinds of
| problems we generate, though the two tools are close enough
| that you definitely want to architect your verification tool to
| be able to use either one (or both at once, in case you hit a
| problem which is pathological in one but not the other).
|
| One place where Z3 exposes a superior interface to CVC5 is when
| you want to do term simplification. CVC5 does not have any real
| analogue to Z3's simplification tactics (like ctx-solver-
| simplify), so if you want to take a term and simplify it with
| respect to a set of assumptions, Z3 is your only choice. I
| think CVC5 has all the machinery you need to implement that
| stuff inside of it, but as a user you can't access it.
|
| The place where CVC5 really pulls ahead of Z3 is when you want
| to produce proofs (eg, to integrate SMT solving into a proof
| assistant like Lean, HOL, or Rocq). Both tools have support for
| generating proofs, but CVC5's are noticeably less buggy, to the
| point that Lean's SMT integration uses CVC5, even though Leo de
| Moura (Lean's designer) was also the original designer of Z3.
| algo_trader wrote:
| What would u recommend for freight/trucking optimiser? not real
| time.
|
| (scaling to 100s-1000s of units)
| y1n0 wrote:
| That's interesting. I'm a logic designer too. How do you make
| use of it?
| wren6991 wrote:
| One of two cases: pushing Verilog through yosys-smtbmc to
| check design assertions/properties, or writing a lil Python
| model of some optimisation trick and checking it's equivalent
| to a more direct implementation.
|
| For the former it's useful when there's already a well-
| defined contract at some interface, like "this bus interface
| follows these basic AHB5 manager rules" or "if x_valid is
| asserted, it remains asserted until x_ready is asserted, and
| the other x_foobar are stable during that time" or "a FIFO is
| never both empty and full".
|
| Simple properties + exhaustive checking is good bang-for-buck
| because it often teases out subtle tangential issues without
| having to write checks for implementation details. This isn't
| "formal verification" per se but using formal checks in a
| lightweight way to help find bugs and inconsistencies in your
| design.
| humam_alhusaini wrote:
| I'm curious as to why Z3 is so much more popular than CVC5 if
| CVC5 is better for solving complex problems. Is it because Z3
| is older?
| Surac wrote:
| Problems solved nothing learned. Poking my problems into a black
| box and getting numbers let me only learn how to poke numbers
| into black boxes
| amelius wrote:
| It's still better than using AI, where even the authors of the
| black box don't really know what they're doing.
| Arainach wrote:
| You learn how to use tools to solve problems and what kind of
| problems those tools can solve.
|
| Using a database or 3D Printer isn't bad because you don't
| learn anything about the internals.
| NooneAtAll3 wrote:
| to be fair that's the general experience with such solvers
|
| step 1: insert the problem
|
| step 2: ???
|
| step 3: profit
| jebarker wrote:
| I wonder how often interviewers object to the approach of solving
| their dynamic programming problem using a constraint solver?
| inerte wrote:
| Like any interview, randomly. Some of them will think it's
| amazing, clever person, chose the best tool for the job. Other
| will think it's weird, person is too clever, chose the worst
| tool for the job.
|
| It totally depends for WHAT you're interviewing, but unlikely
| the company will want Z3-backed code, so most reactions would
| be the later.
| asibahi wrote:
| Previously: https://news.ycombinator.com/item?id=45248558.
| Switched domains since then.
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