Var initialization

[barnjamin]

Problem

Initializing the scratch var seems weird

program = Seq(
  (x := ScratchVar()).store(Int(1)),
  x.load()
 )

what if?

program = Seq(
  v := Var(Int(1)),
  v.load()
 )

Solution

not even PR'ing this, its maybe even weirder

from pyteal import *


class Var(Expr):
    def __init__(self, val: Expr):
        self.val = val
        self.slot = ScratchSlot()
        self.type = val.type_of()
        self.has_stored = False

    def __str__(self):
        if self.has_stored:
            return self.slot.load(self.type).__str__()
        else:
            return self.slot.store(self.val).__str__()

    def __teal__(self, options: CompileOptions):
        if not self.has_stored:
            self.has_stored = True
            return self.slot.store(self.val).__teal__(options)

    def load(self):
        return self.slot.load(self.type)

    def store(self, val: Expr):
        self.val = val
        return self.slot.store(val)

    def has_return(self):
        return False

    def type_of(self):
        if self.has_stored:
            return self.val.type_of()
        else:
            return TealType.none


opts = CompileOptions(mode=Mode.Application, version=6)

program = Seq(v := Var(Int(1)), v.store(Int(2)), v.load())
print(compileTeal(program, mode=Mode.Application, version=6))

[ahangsu]

@jasonpaulos With the introduction of frame pointer, we can probably get started with it, and gradually remove the internal use of scratch slots in current ABI implementation.

What do you think?

Ref: https://github.com/algorand/pyteal/blob/master/pyteal/ast/abi/tuple.py#L75-L76 might benefit from this ticket.

[ahangsu]

I believe this is almost done in functionality, but we might need a set of public interface for allocating such Var object, and potential implication is https://github.com/algorand/pyteal/issues/560

[barnjamin]

took a stab at something https://github.com/algorand/pyteal/pull/643