Name
	n3793, alx-0030r2 - The Elvis operator ?:

Principles
	-  Codify existing practice to address evident deficiencies.

Category
	Avoid multiple-evaluation isses.

Author
	Alejandro Colomar <alx@kernel.org>

History
	<https://www.alejandro-colomar.es/src/alx/alx/wg14/alx-0030.git/>

	r0 (2025-06-24):
	-  Initial draft.

	r1 (2025-12-01; n3753):
	-  Use (opt) syntax.

	r2 (2026-01-16; n3793):
	-  wfix.
	-  Rebase on n3685.

Description
	The expression 'x ? x : y' isn't safe within macros: it
	evaluates 'x' twice.  Some implementations allow omitting the
	second operand of this operator, which results in the same
	semantics, except that the first operand is not evaluated twice.

Prior art
	GNU C.

Proposed wording
	Based on N3685.

    6.5.16  Conditional operator
	@@ Syntax, p1
	 conditional-expression:
		logical-OR-expression
	-	logical-OR-expression ? expression : conditional-expression
	+	logical-OR-expression ? expression(opt) : conditional-expression

	@@ Constraints, p5
	-If
	+If the second operand is specified and
	 one operand
	 is a pointer to a variably modified type
	 and the other operand
	 is a null pointer constant or has type nullptr_t,
	...

	@@ Semantics, p6
	 The first operand is evaluated;
	 there is a sequence point
	 between its evaluation
	 and the evaluation of the second or third operand
	-(whichever is evaluated).
	+(whichever is evaluated,
	+if at all).
	+If the second operand is specified,
	-The second operand is evaluated
	+the second operand is evaluated
	 only if the first compares unequal to 0;
	 the third operand is evaluated only if the first compares equal to 0;
	 the result is the value of the second or third operand
	 (whichever is evaluated),
	 converted to the type described subsequently in this subclause.
	+If the second operand is not specified,
	+the expression behaves
	+as if the first operand were also used as the second operand,
	+except that it is not evaluated twice.