base::ifelse()	ifelse::ifelse1()	dplyr::if_else()	hutils::if_else()	data.table::fifelse()	kit::iif(tprom = TRUE)
is.na(test) replacement	not supported	supported	supported	supported	supported	supported
constraint on typeof(test)	none	none	only "logical"	only "logical"	only "logical"	only "logical"
constraint on class(test)	coercible to "logical"	coercible to "logical"	none	none	none	none
constraint on length(test)	none	none	none	none	none	none
constraint on dim(test)	none	none	none	none	none	none
constraint on typeof(yes|no)	none	none	vector type excluding "expression"	vector type excluding "complex", "list", "expression"; identical	vector type excluding "raw", "expression"; identical or mixture of "integer", "double"	vector type excluding "raw", "expression"
constraint on class(yes|no)	has methods for [, [<-, length, rep (or internal default methods work)	has methods for [, [<-, c, length (or internal default methods work)	vctrs::vec_ptype_common	has methods for ... (or internal default methods work)	identical oldClass(.)	identical oldClass(.) (but not enforced, wrongly)
constraint on length(yes|no)	none	none if strict = FALSE or NA (latter warns); 1 or length(test) if strict = TRUE	1 or if (is.array(.)) k*NROW(test) else length(test)	1 or length(test)	1 or length(test)	1 or length(test)
constraint on dim(yes|no)	none	none	NROW(.) == NROW(test) and more due to vctrs::vec_size_common	none	none	none
typeof(value)	type after subassignment from yes, no to test	type of c(yes, no)	vctrs::vec_ptype_common	common type of yes, no	common type of yes, no	higher of types of yes, no
class(value)	class after subassignment from yes, no to test	class of c(yes, no)	vctrs::vec_ptype_common	class after subassignment from yes to no if length(no) == length(test)	common class of yes, no	common class of yes, no
length(value)	length(test)	length(test)	length of longest argument	length(test)	length(test)	length(test)
names(value)	if (is.atomic(test)) names(test) else NULL	names(test)	splicing of names(yes), names(no)	if (length(no) == length(test)) names(no) else NULL	names(test)	names(test)
dim(value)	if (is.atomic(test)) dim(test) else NULL	dim(test)	dim of longest argument	if (length(no) == length(test)) dim(no) else NULL	NULL	NULL
dimnames(value)	if (is.atomic(test)) dimnames(test) else NULL	dimnames(test)	dimnames of longest argument	if (length(no) == length(test)) dimnames(no) else NULL	NULL	NULL
other attributes	from test if atomic	from c(yes, no)	none	from no if length(no) == length(test)	from first of yes, no not identical to NA	from yes or no or both depending on coercions
support for factors yes, no	none; uses integer representation	full; uses levels(c(yes, no))	full; uses levels(c(yes, no))	partial; requires identical levels(.)	partial; requires identical levels(.)	partial; requires identical levels(.)
support for non-basic S4 classes	full; classes need suitable implementation	full; classes need suitable implementation	none	none	none	none