KOS_OP_MATCH_FIELD_POS_VAR / KOS_OP_MATCH_FIELD_POS_FAST

• Style: EXTRA (LABEL, VAR, RAW) on MATCH_FIELD_POS_VAR, (LABEL, FASTVAR, RAW) on MATCH_FIELD_POS_FAST: label, class, position.

• Stack: [..., o] -> [..., o, a]; jump to a0 with nothing pushed on a miss.

• Semantics: Push the attribute of o, read through Datum, that __match_args__[a2] of the class in the variable a1 names; the variable is read by name on the _VAR form and by fast index on the _FAST form. A missing attribute is a miss. A class with no __match_args__, a __match_args__ that is not a tuple, a position past its end, or an entry that is not a str raises TypeError. On Python 3.9 a dataclass or named tuple without __match_args__ reads the equivalent tuple Python 3.10 would generate.

• Compiler form: Emitted by the match compiler for each positional field of a class pattern; the _VAR form pre-compile, the _FAST twin once convert_fast has lowered the variable.