PreIncrement¶

Status: Stable

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

Description¶

PreIncrement[x] or ++x
    increases the value of x by 1, returning the new value of x.
    ++x is equivalent to x = x + 1.

PreIncrement has attribute HoldFirst. In PreIncrement[x], x can be a
symbol or a Part expression referring to an existing value.
If x has no assigned value, PreIncrement::rvalue is emitted and the
expression is left unevaluated.

Examples¶

No verified examples yet for this function.

Implementation notes¶

builtin_preincrement (++x) calls the shared increment_core(lhs, 1, negate=false, pre=true, "PreIncrement"). The pre=true flag makes it return the new value: it reads the old OwnValue via evaluate, computes and writes back Plus[old, 1] through an evaluated Set (which preserves lvalue shape via Set's HoldFirst), then returns the new value and frees the old. Requires the target to already have an OwnValue, else emits PreIncrement::rvalue and returns NULL. Carries ATTR_HOLDFIRST | ATTR_PROTECTED.

Attributes: HoldFirst, Protected.

Implementation status¶

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

References¶

Source: src/core.c
Specification: docs/spec/builtins/assignment-and-rules.md

Notes & additional examples¶

Worked examples¶

In[1]:= j = 5
Out[1]= 5

In[2]:= ++j
Out[2]= 6

In[3]:= j
Out[3]= 6

Notes¶

++j (PreIncrement) increases j by 1 and returns the new value. It is equivalent to j = j + 1. Contrast with j++, which returns the old value.