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Cannot modify loop variable issue when trying to append something to an array during a loop. #4163

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rockorama opened this issue Jun 22, 2024 · 0 comments · May be fixed by #4164
Open

Cannot modify loop variable issue when trying to append something to an array during a loop. #4163

rockorama opened this issue Jun 22, 2024 · 0 comments · May be fixed by #4164

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@rockorama
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rockorama commented Jun 22, 2024 •
edited by charles-cooper
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Version Information

  • vyper Version (output of vyper --version): 0.4.0
  • OS: osx
  • Python Version (output of python --version): 3.10.0

What's your issue about?

When iterating through an array of addresses, I have to append to another array the ones already processed.
When trying to append to that array I get the compilation error Cannot modify loop variable

It works if I don't iterate through the addresses array, but use indices to do so instead.

@external
def foo():
    remainingToRepay: uint256 = 0
    alreadyDone: DynArray[address, 10] = []
    _assets: DynArray[address, 10] = []
    for a: address in _assets:
        if remainingToRepay == 0:
            break
        if not a in alreadyDone:
            continue
        alreadyDone.append(a)

works with:

  for i: uint256 in range(len(_asserts), bound=MAX_ASSETS):
        a: address = _assets[i]
        if remainingToRepay == 0:
            break
        if not a in alreadyDone:
            continue
        alreadyDone.append(a)
@charles-cooper charles-cooper linked a pull request Jun 22, 2024 that will close this issue
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fix[lang]: fix varinfo comparison charles-cooper/vyper
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@rockorama