Early exit from function with specific for loop construct using MinHeap

[ChewingBever]

V version: V 0.2.4 67e33bf.1be28c5
OS: EndeavourOS Linux

What did you do?

import datatypes { MinHeap }

struct Test {
mut:
    queue MinHeap<string>
    v int
}

fn (mut t Test) buggy() ? {
    for t.queue.len() > 0 && t.queue.peek() ? != '' {
        continue
    }

    t.v = 1
}

fn main() {
    mut t := Test{}

    t.buggy() or {
        eprintln('Error')
        exit(1)
    }

    println(t)
}

I wrote this for loop construct where I both check for the length of the queue & inspect the value of the peek() function.

What did you expect to see?
The for loop should either return an error or properly set t.v = 1. In this specific case, the loop would have to loop zero times.

What did you see instead?
The function exits at the point of the for loop, without returning an error. The result is that the final println call outputs

Test{
    queue: datatypes.MinHeap<string>{
        data: []
    }
    v: 0
}

showing that the function didn't return an error, yet did not execute the final line which sets the value of v.t.
If we replace the for loop with

    for t.queue.len() > 0 {
        if t.queue.peek() ? != '' {
            continue
        }else{
            break
        }
    }

the function does execute as expected, and the value of t.v is set to 1.

[vincenzopalazzo]

Yeah looks like the the for loop works badly with the valuation of the && condition.

This is another example

import datatypes { BSTree }

struct Test {
mut:
    tree BSTree<string>
    v int
}

fn (mut t Test) buggy() ? {
	assert t.tree.is_empty() == true
	for !t.tree.is_empty() && t.tree.min() ? != '' {
		continue
	}

    t.v = 1
}

fn main() {
    mut t := Test{}

    t.buggy() or {
        eprintln('Error')
        exit(1)
    }

    println(t)
}

The following condition !t.tree.is_empty() && t.tree.min() ? != '' should exit when is_empty() is false without evaluating the other side of the end.

Good catch!