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Editorial Team
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Asked: 2026-06-12T10:09:36+00:00

This code runs and produces the output abc : for(10..12){$_=sprintf%x,$_;print} But this code dies

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This code runs and produces the output abc:

for(10..12){$_=sprintf"%x",$_;print}

But this code dies with a Modification of a read-only value attempted at ... error:

for(10,11,12){$_=sprintf"%x",$_;print}

Why are these constructions treated differently?

(This code also works:)

for(10..10,11..11,12..12){$_=sprintf"%x",$_;print}
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1 Answer

  1. Editorial Team

    Probably because of the “counting loop” optimization that comes into play when you foreach over a range. for (1, 2, 3, 4) actually constructs the list (1, 2, 3, 4), containing those particular readonly values, but for (1..4) doesn’t; it just iterates from the start of the range to the end, giving $_ each successive value in turn, and I guess nobody thought it would be worthwhile to match the behavior when you try to assign to $_ that closely.

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