Ok, so I'm completely a newbie with Fantom.

Having got that out of the way... I would like to fill a list (of type "Float?") with nulls. I felt this should work:

List.make( Float?#, 3 ).fill(null, 3)

But this gives me

Invalid args fill(sys::V, sys::Int), not (null, sys::Int)

I tried to explore this with the use of [,] and I am quite confused as to what the story might be:

// These two commands produce a list of the same type
fansh> [,].typeof
sys::Obj?[]
fansh> List.make(Obj?#, 3).typeof
sys::Obj?[]    

// But only one of the two can be filled with nulls
fansh> [,].fill(null, 3)
[null, null, null]
fansh> List.make(Obj?#, 3).fill(null, 3)
ERROR(25): Invalid args fill(sys::V, sys::Int), not (null, sys::Int)

What am I doing wrong with the last command?

All assistance greatly appreciated!

Matthew

Hi Matthew,

Welcome to Fantom!

You may have stumbled on a bug there, for I too would have expected to be able to fill a list with nulls. Brian should be able to verify.

In the mean time, try this:

fansh> list := Float?[,]
[,]
fansh> list.size = 3
3
fansh> list
[null, null, null]

The first line creates an empty list of (nullable) Floats, and the second expands it to a size of 3. The List.size() docs say:

If the size is set greater than the current size then the list is automatically grown to be a sparse list with new items defaulting to null.

This should work

(Float?[,]).fill(null, 3)

In general, you don't ever want to fill using null because arrays already default to null when explicitly resized. So best pattern is:

list := Float?[,]
list.size = 3

The automatically increases it size and makes everything up to size null. You can only increase size of a nullable list though

SlimerDude, thanks for the suggestion that it's a bug. I was pretty confused about this behaviour.

Brian, thanks for the confirmation of this pattern to fill with nulls by specifying the size.

Matthew

@matthew I've not come across this before, what's the difference between:

Float?[,] .fill(null, 3) and

(Float?[,]).fill(null, 3) ???

And why does one syntax allow the list to be filled with null's and other does not!?

As far as I'm aware, they're the same. I'm pretty sure a Type that is before an empty list ( [,] ) is parsed before a dot operator after it.