SameQ¶

Status: Stable

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

Description¶

lhs === rhs or SameQ[lhs, rhs] yields True if lhs and rhs are structurally identical (head-by-head, argument-by-argument), and False otherwise. Numerically equal but distinct heads (e.g. 1 and 1.) are NOT considered same. SameQ tests structure, not value, so unlike Equal it holds for Indeterminate === Indeterminate.

Examples (3)¶

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

Applications (3)¶

In[1]:= a === a
Out[1]= True

In[2]:= 1 === 1.
Out[2]= False

In[3]:= f[x] === f[x]
Out[3]= True

Implementation notes¶

builtin_sameq tests purely structural identity. With fewer than two arguments it returns True by convention; otherwise it compares every argument against the first with expr_eq and returns True only if all are structurally equal, False otherwise. Unlike Equal, there is no numeric coercion — 1 === 1. is False — and it never returns NULL (the result is always a definite boolean).

Unlike Equal, SameQ never stays symbolic and does not coerce numeric types, so 2 === 2.0 is False.
Also unlike Equal, SameQ compares structure rather than value, so Indeterminate === Indeterminate is True.

Attributes: Protected.

References¶

See also: Equal

Source: src/comparisons.c
Specification: docs/spec/builtins/comparisons.md
Tests: tests/test_comparisons.c
Tests: tests/test_dsolve.c
Tests: tests/test_hermitian_matrix_q.c
Tests: tests/test_parse.c

Notes & additional examples¶

Notes¶

SameQ (===) is a structural test that always returns True or False. Numerically equal but distinct heads, such as 1 (Integer) and 1. (Real), are not the same.