Attributes

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

Attributes[s]

gives the list of attributes for s.

Examples (4)

Every input below was run against the current Mathilda build and its output recorded.

Basic examples (1)

In[1]:= Attributes[Plus]
Out[1]= {Flat, Listable, NumericFunction, OneIdentity, Orderless, Protected}

Applications (3)

The full bundle an arithmetic head carries

In[2]:= Attributes[Plus]
Out[2]= {Flat, Listable, NumericFunction, OneIdentity, Orderless, Protected}

A listable numeric function

In[3]:= Attributes[Sin]
Out[3]= {Listable, NumericFunction, Protected}

HoldAll collapses the HoldFirst and HoldRest bits into one token

In[4]:= Attributes[Hold]
Out[4]= {HoldAll, Protected}

Implementation notes

builtin_attributes (src/attr.c) reads the symbol's attribute bitflags via get_attributes(name) and builds a List of attribute symbols from them, e.g. ATTR_FLAT -> Flat, the HoldFirst|HoldRest pair collapsing to HoldAll, ATTR_LISTABLE -> Listable, ATTR_PROTECTED -> Protected, etc. The symbol itself is held unevaluated (Attributes carries ATTR_HOLDALL).

• Common attributes include Flat (associativity), Orderless (commutativity), Listable (automatic threading over lists), HoldFirst, HoldRest, HoldAll (evaluation control), and Protected.

Attributes: HoldAll, Protected.

References

See also: Flat, Orderless, HoldFirst, HoldRest, HoldAll

• Source: src/attr.c
• Specification: docs/spec/builtins/expression-information.md
• Tests: tests/test_algebraicnumberdenominator.c
• Tests: tests/test_algebraicnumbernorm.c
• Tests: tests/test_algebraicnumberpolynomial.c
• Tests: tests/test_algebraicnumbertrace.c

Notes & additional examples

Notes

Attributes[sym] returns the sorted list of attribute symbols set on sym, read from its attribute bitflags. The HoldFirst | HoldRest pair is reported as the single token HoldAll; Protected marks every builtin.

Attributes holds its argument (HoldAll), so the symbol is not evaluated first — you get the attributes of sym itself, not of its value. Set and clear them with SetAttributes and ClearAttributes.