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Re^3: return of hash-assigment in list context (the fix)

by LanX (Canon)
on Jan 02, 2013 at 22:06 UTC ( #1011364=note: print w/ replies, xml ) Need Help??


in reply to Re^2: return of hash-assigment in list context (bug?)
in thread return of hash-assigment in list context (bug?)

Thx, this one looks good! =)

2010-09-11 David Mitchell
list cxt hash assign with dups gives garbage

the others are too new.

Fix for #31865: weird results from reverse( %x = reverse %h )

Basically, anything of the form

@a = %h = (list with some duplicate keys)

may have left @a containing weird and/or freed values.

There was a partial fix for this with ca65944e, but it was broken (it did one big block move on the stack at the end to remove duplicates, but duplicates weren't necessarily all in one block.)

The new fix is a two-stage process. First, while pulling key/value pairs of the stack and assigning them to the hash, each key/val pair is written back to the stack - possibly at a lower position if there are duplicates to be skipped.

Finally at the end if any duplicates have been detected, then in list context, a single pass is made through the stack, and for each key/val pair, the key is looked up and the val on the stack is overwritten with the new value (replacing possibly freed or other garbage values).

Cheers Rolf


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