Ternary operators

[skejeton]

Ternary operators

[skejeton]

The syntax is up to choice here, we could do something like this, gdscript inspired:

fn max(a, b: int) {
  return b if a < b else a
}

(notice the check expression is now in the middle)

[vtereshkov]

I like this proposal. As for the syntax, I think that b if a < b else a is very hard to compile for a single-pass compiler that generates bytecode on-the-fly. The compiler sees b but does not know whether to insert a jump instruction before it to skip this b if a < b yields false.

[marekmaskarinec]

I would like ternary operators in umka. There are a lot of cases where they would be useful. As for the syntax proposed by @vtereshkov, I think it would imply that switch statement s and maybe even loops support this syntax too. Something to think about?

[vtereshkov]

There is an unexpected issue with reference counting that we need to solve before we can implement the ternary operator. Consider the following code:

        for i := 0; i < 2; i++ {
                // ...
                p = i % 2 == 0 ? new(int, 42) : new(int, 43)
                // ...
        }

Since every reference-counted function result is stored in a temporary local variable to prevent its premature death, the actually executed pseudocode is like this:

        for i := 0; i < 2; i++ {
                // ...
                p = i % 2 == 0 ? {__temp0 = new(int, 42); __temp0} : {__temp1 = new(int, 43); __temp1}
                // ...
                decref(__temp0)
                decref(__temp1)
        }

This means that, e.g., __temp0 will get some reference-counted value only once (at iteration 0), but have its reference count decremented twice (at iterations 0 and 1). It may cause a dangling pointer.

Notice that we cannot call decref(__temp0) immediately in the innermost {} block, since __temp0 must at least outlive the assignment to p.