Putting code with side effects into an assert is asking for trouble. Compile with NDEBUG set and the effects mysteriously disappear! Anything beyond an equality expression or straight boolean should be avoided.

▲ samiv 3 hours ago | parent | next [-]

That's why you define your own assert macro and keep in on unconditionally. Your programs will be better for it.

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jandrewrogers 2 hours ago | parent [-]

An assertion can be arbitrarily expensive to evaluate. This may be worth the cost in a debug build but not in a release build. If all of assertions are cheap, they likely are not checking nearly as much as they could or should.

	▲	samiv 2 hours ago \| parent [-]
		Possibly but I've never seen it in practice that some assert evaluation would be the first thing to optimize. Anyway should that happen then consider removing just that assert. That being said being slow or fast is kinda moot point if the program is not correct. So my advisor to leave always all asserts in. Offensive programming.

▲ usrnm 4 hours ago | parent | prev | next [-]

I once spent several days debugging that same mistake. Stuff worked perfectly in tests but broke misteriously in production builds. Couldn't stop laughing for a few minutes when I finally figured it out.

▲ maccard 3 hours ago | parent | prev | next [-]

Indeed.

   bool is_even(int* valPtr) {
      assert(valPtr != nullptr);
      return *valPtr % 2;
    }

Does not do what you think it does with nullptr. A major game engine [0] has a toggle to enable asserts in shipping builds, mostly for this reason

[0] https://dev.epicgames.com/documentation/en-us/unreal-engine/...

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mhh__ 2 hours ago | parent | next [-]

This is a very "Dr Dr it hurts when I do this" "Don't do that" one it must be said.

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dccsillag 3 hours ago | parent | prev | next [-]

I'm sorry, but what exactly is the problem with the code? I've been staring at it for quite a while now and still don't see what is counterintuitive about it.

	▲	IshKebab 3 hours ago \| parent [-]
		There's nothing wrong with it. It does exactly what you think it does when passed null.

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secondcoming 44 minutes ago | parent | prev [-]

Let's not vague post on HN. What's the problem with the above?

▲ nyc_pizzadev 5 hours ago | parent | prev | next [-]

This is just a symptom of a bad assert() implementation, which funny enough is the standard. If you properly (void) it out, side effects are maintained.

https://github.com/fiberfs/fiberfs/blob/7e79eaabbb180b0f1a79...

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omoikane 5 hours ago | parent [-]

assert() is meant to be compiled away if NDEBUG is defined, otherwise it shouldn't be called assert(). Given that assert() may be compiled away, it makes sense not to give it anything that has side effects.

Abseil has the convention where instead of assert(), users call "CHECK" for checks that are guaranteed to happen at run time, or "DCHECK" for checks that will be compiled away when NDEBUG is defined.

https://github.com/abseil/abseil-cpp/blob/0093ac6cac892086a6...

	▲	nmilo an hour ago \| parent [-]
		If your assert compiles down to `if (condition) {}` in production then the compiler will optimize away the condition while keeping any side effects.

▲ jmalicki 5 hours ago | parent | prev | next [-]

Side effects are bad of course, but anything beyond a straight boolean or equality is bad?

`assert(vector.size() < 3)` is ridiculous to you?

▲ andrepd 35 minutes ago | parent | prev | next [-]

Rust has assert and debug_assert, which are self-explanatory. But it also has an assert_unchecked, which is what other languages incl C++ call an "assume" (meaning "this condition not holding is undefined behaviour"), with the added bonus that debug builds assert that the condition is true.

▲ nealabq 4 hours ago | parent | prev [-]

I don't mean to be that guy, but for "functional" programmers a print statement has "side effects".

But your meaning is clear. In an assert expression, don't call functions that might change the program/database state. Be as "const" as possible.

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toxik 3 hours ago | parent [-]

Not just for functional programmers. Prints and other I/O operations absolutely are side effects. That's not running counter to the point being made. Print in an assert and NDEBUG takes away that behavior.

	▲	nealabq 17 minutes ago \| parent [-]
		You're right of course. I was thinking specifically of printing log/debug statements in the assert(..), but that usually only happens if the assert(..) fails and exits, and in that case the "no side effects" rule no longer matters.