PyTEAL: Increment slot value in a Seq expression

1

How I can increment a slot value by 1 without PyTEAL compiler yelling about store/load order?

e.g:


def verify():
    verify_from = Txn.application_args[0]
    verify_to = Txn.application_args[1]
    bitfield = ScratchVar(TealType.uint64, SLOTID_VERIFIED_BITS)
 
    return Seq([Assert(And(is_proper_group_size(),
                       Txn.group_index() < Global.group_size(),
                       Txn.group_index() > Int(0),
                       Btoi(verify_to) > Btoi(verify_from),
                       Txn.sender() == App.globalGet(Bytes("vphash")))),
                bitfield.store(bitfield.load() + Int(1)),
                Approve()])

It wont me let to do bitfield.store(bitfield.load() + 1), but this should be pretty “transpilable” to TEAL without problems. Should be noted that bitfield is a fixed slot at position SLOTID_VERIFIED_BITS.

Thanks in advance.

2

I added a comment on your Issue to handle that too.

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3

I believe this is a different problem from the linked github issue. Right now PyTeal has a strict requirement that a scratch slot cannot be loaded unless it has a value stored in it first, and I believe that’s the problem here.

If you were to add bitfield.store(Int(0)) somewhere before that section of code is called, it should fix the issue.

Though I recognize this constraint can be a bit annoying, since it’s sometimes useful to rely on the default value of 0 for scratch slots. Let us know if you think this safety check should be somehow made optional or turned into a warning instead.

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4

Maybe this is necroposting, but Jason, you are right. Storing the value first made it work. Thank you!

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