Spurious nil table keys during iteration

[TheCount]

When iterating over a runtime.Table using the Next() method, I occasionally get a nil key return value with ok == true.

I can try putting together a minimal example of the bug, however, looking at the source code, I see this:

golua/runtime/hashtable.go

Line 361 in 4f77264

return NilValue, NilValue, true

This looks like it should be return NilValue, NilValue, false instead in the first if. Could this already be the fix?

[arnodel]

It is possible to get a nil key return value and for ok to be true. The returned value ok is true if the key passed in to Next is valid (i.e. is present in the table), but if it is the last key in the table then then there is no next key - value so what is returned is NilValue, NilValue, true (this is what happens in the line you refer to).

For example if a table t has one item in it with key = "hello" and value = 42 then

• calling t.Next(nil) returns "hello", 42, true
• calling t.Next("hello") returns nil, nil, true

(syntax above is not quite correct because I should write rt.NilValue instead of nil, etc)

If you encounter another type of situation then please give me an example so that I can understand and fix the issue.

[TheCount]

Aah, thank you for this explanation, that makes a lot of sense.

The thing that threw me off is that often in Go, a bool return value like this indicates whether there is another entry.

I'd like to suggest to extend the documentation of Table.Next a bit to make all of this clearer, maybe something like the following?

// Next returns the key-value pair that comes after k in the table t.
// If k is NilValue, the first key-value pair in the table t is returned.
// If k is the last key in the table t, a pair of NilValues is returned.
// If the table t is empty, the returned key-value pair is always a pair of NilValues, regardless of k.
// In all cases, ok is true if and only if k is either NilValue or a key present in the table t.

Thanks again!