[BUG] Unexpected copy-on-write behaviour with for loops

[hypno2000]

Bug description

this code:

from collections import InlineArray

def main():
    bits = byte_as_bits(137)
    print("Bits: ", bits)

def byte_as_bits(byte: UInt8) -> String:
    var bits = InlineArray[UInt8, 8](0, 0, 0, 0, 0, 0, 0, 0, 0)
    for i in range(8):
        print("Before: ", byte)
        bits[i] = byte & 1
        byte >>= 1
        print("After:  ", byte)

    var bits_string = String()
    for i in range(8).__reversed__():
        bits_string += str(bits[i])

    return bits_string

outputs:

Before:  137
After:   68
Before:  137
After:   34
Before:  137
After:   17
Before:  137
After:   8
Before:  137
After:   4
Before:  137
After:   2
Before:  137
After:   1
Before:  137
After:   0
Bits:  11111111

It is strange how the byte variable on the "After" print is changing but it keeps its original value in the "Before" print. On every iteration cycle it takes a copy from the original argument but the second print it seems to be a value that was copied only once and is changed with every cycle.

When we assign byte to our own variable before the loop then everything looks good and the return value is also correct:

from collections import InlineArray

def main():
    bits = byte_as_bits(137)
    print("Bits: ", bits)

def byte_as_bits(byte: UInt8) -> String:
    var bits = InlineArray[UInt8, 8](0, 0, 0, 0, 0, 0, 0, 0, 0)
    var my_byte = byte
    for i in range(8):
        print("Before: ", my_byte)
        bits[i] = my_byte & 1
        my_byte >>= 1
        print("After:  ", my_byte)

    var bits_string = String()
    for i in range(8).__reversed__():
        bits_string += str(bits[i])

    return bits_string

Before:  137
After:   68
Before:  68
After:   34
Before:  34
After:   17
Before:  17
After:   8
Before:  8
After:   4
Before:  4
After:   2
Before:  2
After:   1
Before:  1
After:   0
Bits:  10001001

System information

- MacOS 15.2 (24C101)
- mojo 25.1.0.dev2025011705 (92b12ebe)
- magic 0.6.2 - (based on pixi 0.40.0)