SetAttributes

Turns on one of the Wolfram-named properties Attributes can report.

✓ checked against that system · ! checked, with disagreements (hover a chip)Wolfram LanguageSetAttributes!

SetAttributes(f, attr)Turns

attr

on for

f

's operator definition, in place.

SetAttributes(f, {attr1, attr2, ...})Turns on several attributes at once.

Typed signatures

Type	Package	Applies
`(symbol, any) -> any`	`combinatorics`	always

Domain: Collections

Details

Only $\{Flat, HoldAll, Listable, Orderless\}$ can actually be turned on — see Attributes for why those four and no others. Declines (stays unevaluated) for an undeclared $f$ , or any attribute name outside that set, rather than silently accepting a change that didn't happen.
A declared head is Protected: SetAttributes leaves the call unevaluated and says SetAttributes::write (Tag f in f is Protected.), where Wolfram, whose Protected guards definitions rather than attributes, makes the change. Only a symbol of your own, defined first, takes attributes.
Always returns $Nothing$ , like Wolfram's own $Null$ .

Examples

Basic #

define a head of your own, turn Orderless on, then read it back with Attributes

\mathrm{Last}(\bigl\lbrack\mathrm{userHead}(x)\coloneq x, \mathrm{SetAttributes}(\mathrm{userHead}, \mathrm{Orderless}), \mathrm{Attributes}(\mathrm{userHead})\bigr\rbrack)

Out

\bigl\lbrack\mathrm{Orderless}\bigr\rbrack

Wolfram needs no definition before a symbol takes attributes; here the head is defined first, since SetAttributes leaves an undeclared symbol alone.

a declared head is Protected: the call stays unevaluated and says SetAttributes::write

\mathrm{SetAttributes}(\mathrm{HarmonicMean}, \mathrm{Orderless})

Out

\mathrm{SetAttributes}(\mathrm{HarmonicMean}, \mathrm{Orderless})

Properties #

\mathrm{Attributes}(\mathrm{SetAttributes})

Out

\bigl\lbrack\mathrm{HoldAll}, \mathrm{Protected}\bigr\rbrack

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