interpolated string not evaluating in assert?

[toolateralus]

consider this code:

assert false, "Parsing failed: ${err}"

my question, is it expected and acceptable that when this fires, it prints:

FAIL: fn main.main: assert false, 'Parsing failed: $err'

I feel like that is completely unintuitive, I'm not certain as to why a runtime assertion wouldn't evaluate its both of it's operands, unless
it's stated somewhere that the second argument side of an assert has to be a compile time constant? And if the latter is the case, then why didn't the compiler give me an error or warning about it?

Also, sorry if they're not called "interpolated strings", I've just started learning the language, and that's what I know them as.

I'm considering creating an issue about this, but I'm not certain that this warrants it.

[jorgeluismireles]

Your line will work if there exist err variable like in next program.

fn divide(a int, b int) ! int {
	if b == 0 {
		return error('denominator can\'t be zero')
	}
	return a/b
}

fn main() {
	q := divide(10, 0) or {
		assert false, 'divide error: ${err}'
		0
	}
	dump(q)
}

https://play.vlang.io/p/cb4fa0ac1d

code.v:10:NaN: fn main.main: assert false, 'divide error: $err'
      message: divide error: denominator can't be zero
V panic: Assertion failed...

The divide function returns a Result, that is, a possibility of a value or an error (when denominator is zero). By calling the divide function the compiler requires an or { ... } block where to go when the error is triggered, inside the block err variable is the string returned as Result denominator can\'t be zero and is interpolated as a message. An alternative is use a panic('divide error:${err})

[toolateralus]

Thanks for the reply, total doh moment xd

[toolateralus]

I looked back at my code, and the function I was calling into:

mut n_lines := 0
bitcodes := parse(mut &lines, mut &n_lines) or {
  assert false, "Parsing failed, ${err}"
  return
}

only returns errors in that exact form, error(...) or return error("My error message!") or whatever

Am I totally missing something from your explanation, or is it still expected that this prints "Parsing failed, $err"

[jorgeluismireles]

Try to write a test for your function parse with controlled parameters and asserting for a particular expected err string inside the or block. Is not too common but sometimes the compiler could fail for complicated combinations and then you can issue a problem with a reduced code.