Tcl Source Code

Doing: [scan 0.99 %d.%d.%d.%d a b c d] returns 2 and
only variables a and b are set. Variable c and d are
not being touched. If these variables did not exist
before, they still don't exist after the operation.
Otherwise they will still have their old value.

According to the manual page: "If no varName variables
are specified, then scan works in an inline manner,
returning the data that would otherwise be stored in
the variables as a list".

From this information I expect [scan 0.99 %d.%d.%d.%d]
to return a list with two elements. However, the
command returns a list with four elements: 0 99 {} {}

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That next line refers to the fact that [scan "" %d.%d.%d.%d]
returns an empty string and not a list of four empty
strings. That is actually consistent with the expected
result I described.

The only situation that is inconsistent is a partial match.
I have seen the code and noticed that it intentionally adds
empty list entries. But that doesn't automatically make it
the right thing to do.

I do realize that this is unlikely to be changed because
that might break existing code that accounts for the current
behavior. So probably the only thing that can be done now is
to warn people about this illogical behavior in the manual page.

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Note that the next sentence is "In the inline case, an empty
string is returned when the end of the input string is
reached before any conversions have been performed.", and
perhaps that needs augmenting to say that each %-sub that
goes unmatched also makes an empty string.  Inline scan does
intentionally operate to return a list equal in length to
the number of %-subs.

File Added - 157677: scan.patch