fix: make last(empty) yield no output values #3179
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itchyny
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mousetail
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Sep 18, 2024
wader
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Sep 23, 2024
src/builtin.c
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| @@ -1879,6 1879,32 @@ BINOPS | |||
| #undef LIBM_DD | |||
| #undef LIBM_DA | |||
|
|
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| // This is a hack to make last(empty) yield no output values without using boxing. | |||
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Maybe should say "last(g) where g does not output any value" so that it does not sound like it's a special case for exactly argument "empty"?
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I fixed the comment.
wader
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Sep 23, 2024
| BLOCK(gen_op_bound(LOADVN, is_empty_var), | ||
| gen_op_target(JUMP_F, if_empty), | ||
| if_empty, | ||
| gen_op_bound(LOADVN, last_var))); |
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Trying to understand what kind of "pesudo"-jq this translates, will
last(g)be something like (vm is not limited by scoping rules?)
( true as $is_empty
| ( g as $last
| false as $is_empty
| empty
)
// if $is_empty then empty else $last end
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Closer to write with reduce;
def last(g): reduce g as $item (
{ last: null, is_empty: true };
.last = $item | .is_empty = false
) | if .is_empty then empty else .last end;
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wader
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This patch fixes
last/1to produce no output value when the argument yields nothing. For example,[last(empty)]and[last(range(0))]now produce[]instead of[null]. I fixed the issue using byte-coded definition, to avoid unnecessary value boxing. This closes #1869.